The 1990 game of the year is Super Mario World.
The runner up is The Secret of Monkey Island.
The master thread for all of these contests can be found here.

What do you believe to be the "Game of the Year" for 1990 and why?  Also, vote on "Game of the Year" for 1990. 

Michael Jackson’s Moonwalker (Arcade/Genesis/Home Computers)
In 1990, three completely different versions of Michael Jackson’s Moonwalker were released: one for the arcade, one for the Genesis and a third for home computers.  Sega developed and published both the arcade and Genesis version while U.S. Gold published the version for home computers.  All versions of the game were in some way inspired by the Smooth Criminal video that came from the Moonwalker movie.

Arcade version:  https://www.youtube.com/watch?v=Ku8oaK_iEwk
Computer version:  https://www.youtube.com/watch?v=c0xPDFxlN0I
Smooth Criminal video:  https://www.youtube.com/watch?v=h_D3VFfhvs4

Sid Meier’s Railroad Tycoon (Home Computers)
Another hit game from the guy who puts his name on everything.  It was also the first game with the word Tycoon in the title.

Wing Commander (PC)
Chris Roberts brings combat and flight simulation to outer space.  Wing Commander was about 5 times more expensive to create than most other computer games at the time, and inspired many other computer games of the era to increase their budgets.  This first version of the game had 2 expansion packs and inspired 4 more sequels.  It also inspired competitors to make space combat games like X-Wing.

The Secret of Monkey Island (Home Computers)
Ron Gilbert, Dave Grossman and Tim Schafer design this hilarious adventure game from LucasArts.  The Secret of Monkey Island went on to release 5 more sequels. 

Dr Mario (NES/Gameboy/Arcade)
After Tetris, the next biggest action puzzle game of this era was Dr Mario.  Dr Mario would go on to sell 5.34 million copies on the Gameboy and 4.85 million copies on the NES.

Dragon Quest 4 (NES)
Dragon Quest mania continues in Japan with Dragon Quest.  DQ4 is often considered the best RPG on the NES as it’s gameplay and storytelling seem much more sophisticated compared to other NES RPG’s.  However, it wasn’t released in North America until 1992 making it overshadowed by the 16-bit systems by that time.  DQ4 went on to sell over 3.1 million units in Japan alone.

Mega Man 3 (NES)
The Blue Bomber returns with his canine sidekick, Rush.  Mega Man 3 would sell over 1 million copies on the NES.

F-Zero (SNES)
Why fool with F-1 racing when you can play F-Zero?  This SNES launch game is still popular today with the recent release of F-Zero 99.  F-Zero went on to sell over 2.8 million copies worldwide.

Super Mario World (SNES)
Mario goes 16-bit and gets Yoshi.  The original Super Mario team of Shigeru Miyamoto, Takashi Tezuka and Koji Kondo are joined by several other members as team sizes grow for the 16-bit era.  This launch title was commonly bundled with the SNES and went on to sell over 20.6 million copies worldwide.

TV Commercials:  https://www.youtube.com/watch?v=utkuzMlw8Dw

Other (please specify)
If you think another games deserves to be "Game of the Year" other than one of the 9 I listed above, then please vote “Other” and say your game in the comments.  If the "Other" category takes at least 2nd place and no other game gets at least 50% of the vote, then I will do a runoff vote including the most mentioned game(s) from the comments.

The winner of this vote will be decided Saturday, Sept 30 at 11:59 EST.

Here are some other notable games from 1990:

Ultima 6 (Home Computers)
Speedball 2 (Home Computers)
Chip N Dale Rescue Rangers (NES)
Crystalis (NES)
Final Fantasy III (NES)
Ninja Gaiden 2 (NES)
Super C (NES)
Gun Nac (NES)
F-1 Race (Gameboy)
TMNT: Fall of the Foot Clan (Gameboy)
Pilotwings (SNES)

I went with Super Mario world because if you asked me in 1990 that would of been my vote. That being said the most important game for future of PC gaming that was released in 1990 was Commander Keen in Invasion of the Vorticons as it was a side project of John Carmack and it success led John Carmack and others to quit working for Softdisk and create ID software which went on to basically create the FPS genre with Wolfenstein 3d and made it mainstream with Doom. Commander Keen also a fun game on it own and another example of John Carmack genius because smooth side scrolling games really only existed on consoles and not PC before he created a way to do it on PC. He actually originally created the code to try to sell Nintendo on porting Mario to PC but Nintendo was not interested so he made Commander keen instead.

This is actually a difficult year for me to decide. I love the point and click adventure genre (with high focus on humor) that The Secret of Monkey Island made popular.
Usually I judge a game based on how likely I am to pick it up and play today. By that metric Super Mario world is the winner since it is still a blast to play.
But I feel that in the case of story driven games that metric is not as fair. The game will pretty much never be as good as the first time it is played since a majority of the enjoyment comes from not knowing.

The vote goes to The Secret of Monkey Island this time. An exceptional game with a massive impact that might be the first time a video game made me laugh out loud something only a handful of games have succeeded in, can only think of Conker as another example even if Ace Attorney and the Mario and Luigi games came close.

I vote for The Secret of Monkey Island! Which was also my personal favorite '90 game. It absolutely oozes personality and charm from its very first moments straight through to the end. More than any other really, this is the title that first got me into computer gaming.

Like I was saying on the '89 thread, when my parents finally caved and got me a Sega Genesis with Golden Axe for my eighth birthday in 1990, they started getting concerned about the terribly violent nature of the games I was into (), so they tried to steer me toward computer gaming on the thinking that it was more educational just in general. Had that reputation. First game they got me was Where in Time is Carmen Sandiego?, which I actually wound up liking. (Evidently a lot of other people did too, as it was actually the best-selling game of the 1989 holiday season, apparently.) The Carmen Sandiego classics aren't entirely as fun for me nowadays, as the knowledge they imbue is kind of rudimentary at this point in life, but it was kind of a fun way for a kid to learn some basic facts about history and other topics back when. Other early, somewhat less memorable entries in my compulsory computer gaming library included Midnight Rescue and Number Munchers. (My dad at least had the decency to get me Gods the next year, but that was very much the exception to the rule.)

The Secret of Monkey Island though was special in its rich atmosphere, lack of basicness and pretention. I quickly came to love its world, characters, music, and sense of style. It made me laugh. A lot. And still does. The Carmen Sandiego franchise exempted, computer gaming at first felt kind of boring to me; like something my parents were just forcing me into. The Secret of Monkey Island though was the game that proved computer gaming could be just as fun as console gaming, if not more so. Simply a platform with perhaps different strengths.

I also can't pass up the opportunity to give F-Zero a shout-out because it was awesome and my favorite racing game on the Super NES and also of the whole era. An early effort to prove the power of the Super NES with its Mode 7 graphics, its futuristic ambience proved of instant appeal to a generation of gamers that included me when I finally got it a couple years after this.

I'm also gonna give a shout-out to the open-ended action-platformer platformer from this year, Clash at Demonhead, which, along with The Guardian Legend, is another top NES favorite of mine today. Since far too many people missed this little gem back in the day, here's Clash at Demonhead:

EDIT: Oop, actually Clash at Demonhead was originally released IN JAPAN in 1989, I just discovered. I did not know that. Had just gone with the American version's release date. *shrugs* Oh well, I'm leaving the shout-out here anyway.

Difficult choice.

I played Railroad Tycoon a lot, it was a very addictive building sim. I still know you could place 32 signals max to optimize the network, as well as max number of trains that could be running. It was so cool to see the cities grow over time after you connect them to the network, the landscape slowly changing from pastoral little villages to mega cities on the busy junctions.
Priority missions were fun to make some extra cash, get an express to deliver something asap by rerouting and stopping other traffic in the way. Then you had rivals you could start delivery wars with to win the rights over stations to expand your territory. Basically flooding those stations with products while making sure to always have trains standing by to hover up all cargo.
The best of all was making things run like clockwork, upgrading goods from mine/farm to bulk processing to factories to sell in cities with the highest demand. Yet mines would deplete over time so the work was never done. While in the late stage cities were big enough to shift money making to passengers and mail express trains.

This year also birthed Stunts

A game I played for many years just like Railroad Tycoon. The track editor was amazing and I made tracks with ridiculous jumps abusing the max speed glitch in one of the cars.

The Secret of Monkey Island totally blew me away at the time. I first played it at my friend's house on Amiga 500, then got a copy for PC. From text based entry to point and click, Monkey island made the transition flawlessly. It's such an influential game it's still remade and now already has a second appearance / season on Sea of Thieves. I played the remake while switching back and forth between the old and new style, I wish all remakes had that option :) Plus it was the first game that gave me ear worms, the music is still stuck in my head :)

My vote goes to Monkey Island.

Super Mario World - the best 2D Mario baby ;)

Another year that an excellent Mega Man game loses to Mario. Super Mario World remains my favorite Mario game of all time. The game felt like SMB3 on steroids and brought a whole new cast of enemies as well as Yoshi. The cape was an incredible power-up (almost too incredible) and the ability to throw items/enemies up added great ideas in gameplay - a feature that has finally returned in the upcoming Super Mario Bros Wonder.

The colorful graphics, excellent sound effects and wonderful world along with its humor and whimsy make it my game of 1990 by a wide margin. It's simply one of the most enjoyable games you can play.

TSoMI

To begin with, Wing Commander is my absolute favorite game/series ever, period. I'm so happy to see it there, that I didn't have to put it as Other as I would have.

Secondly, 1990 is my favorite year of games. Aside WC there's Monkey Island (another of my top 5 series ever and the first is my favorite) and DQ4 which I consider the best Nes game ever. And I do think Phantasy Star III is underrated, I like it at least as much as the second.
Other list is missing Loom, a beautiful game, perhaps my second favorite Lucas adventure after MI. Another personal favorite of the year is D&D dragon flight sim DragonStrike, And speaking of flight sims, Red Baron.
Sega had roguelike Dragon Crystal/Fatal Labyrinth that I still play annually on my MS. Another MS favorite of mine is Slap Shot (it may be the game I've had longest aside the build-in).
King's Quest V isn't a personal favorite but worth mentioning.
Star Control is still fun.
And Minesweeper and Solitaire appeared same year, from certain perspective big games.