The 2018 Game of the Year is Super Smash Bros Ultimate.
The runner up is God of War.
The master thread for all of these contests can be found here.

The Switch had an amazing launch year, but its offerings seemed kind of weak in 2018 until the end of the year.  However, the PS4 had strong releases throughout all of 2018.  The XBox One also ran.  Without further ado, here is the list of games for 2018:

Among Us (PC/Mobile)
This Mafia/Werewolf style game released in 2018 to very little fanfare.  However, during the 2020 pandemic lockdowns it became one of the most played games in a year when everyone was playing games.  By the end of 2020 over 500 million people had played Among Us.

Celeste (Switch/PS4/XB1/PC/Mac/Linux)
Celeste is named after the mountain and not the girl climbing it.  This puzzle platformer was a hit with critics with scores ranging from 88-94 on Metacritic.  Celeste has sold over 1.5 million units on Steam alone.

Dead Cells (Switch/PS4/XB1/PC/Mac/Linux)
One thing that got Dead Cells notoriety was the fact that IGN copied their review from Boomstick Gaming.  However, it also happened to be a really good game.  Dead Cells scored an 87-91 on Metacritic and has sold over 10 million copies.

God of War (PS4)
Kratos gets a reboot in a variety of ways including joining the Norse mythology instead of the Greek.  God of War scored an impressive 94 on Metacritic and has sold over 23 million copies to date.

Monster Hunter World (PS4/XB1/PC)
Before 2018, Monster Hunter was extremely popular in Japan but was a niche franchise in the rest of the world.  That all changed with the release of Monster Hunter World which had most of its sales outside of Japan.  Monster Hunter World has sold over 20 million copies and scored an 88-90 on Metacritic.

Red Dead Redemption 2 (PS4/XB1)
Rockstar strikes again with this open-world Western game releasing five years after GTA V.  Red Dead Redemption 2 scored an amazing 97 on Metacritic and has sold over 55 million copies.

Spider-Man (PS4)
Spider-Man games go all the way back to the Atari 2600, but this entry is the first time it became one of Sony’s first-party IP.  This open world game went on to sell over 33 million copies.

Octopath Traveler (Switch)
Square-Enix completely underestimated how popular this retro HD-2D RPG would be.  Physical copies were unavailable for most to purchase for the first two weeks after its initial release in Japan, because there weren’t nearly enough physical copies available.  Octopath Traveler went on to sell over 3 million copies total.

Super Smash Bros Ultimate (Switch)
Everyone is here!  Nintendo amazed everyone by announcing that their latest entry would include every character ever in Smash and more.  They went on to release even more characters in the following years through DLC.  SSBU scored a 93 on Metacritic.  It has sold over 32.4 million copies and is still going strong.

Other (please specify)
If you think another game deserves to be "Game of the Year" other than one of the 9 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 40% of the vote, then  there will be a runoff vote including the most mentioned game(s) from the comments.

Voting for 2018 Game of the Year will end on Thursday, Dec 21 at 11:59 PM, EST.

Here are some other notable games from 2018:

CrossCode (PC/Mac/Linux)
Pillars of Eternity II: Deadfire (PC/Mac/Linux)
Return of the Obra Dinn (PC/Mac)
Rimworld (PC/Mac/Linux)
Unavowed (PC/Mac)
Assassin's Creed Odyssey (Switch/PS4/XB1/PC)
Astro Bot Rescue Mission (VR)
The Banner Saga 3 (Switch/PS4/XB1/PC/Mac)
Call of Duty: Black Ops 4 (PS4/XB1/PC)
Detroit: Become Human (PS4/XB1/PC)
Dragon Ball FigherZ (PS4)
Dragon Quest Builders 2 (Switch/PS4)
Far Cry 5 (PS4/XB1/PC)
Forza Horizon 4 (XB1/PC)
Full Metal Furies (Switch/XB1/PC)
Guacamelee! 2 (Switch/PS4/PC)
Iconoclasts (Switch/PS4/Vita/PC/Mac/Linux)
Judgement (PS4)
Monster Boy and the Cursed Kingdom (Switch/PS4/XB1)
Ni No Kuni II: Revenant Kingdom (PS4/PC)
Subnautica (PS4/XB1/PC/Mac)
Shadow of the Tomb Raider (PS4/XB1/PC)
Trails of Cold Steel IV (PS4)
Valkyria Chronicles 4 (Switch/PS4/XB1/PC)
Into the Breach (Switch/PC/Mac)
Kirby Star Allies (Switch)
Labo (Switch)
The Messenger (Switch)
Pokemon Let's Go: Pikachu/Eevee (Switch)
Super Mario Party (Switch)
Xenoblade Chronicles 2: Torna-The Golden Country (Switch)

A number of great games this year as well, yet the winner for me is fairly easy to pick once again. I'll have to vote other for Trails of Cold Steel IV. Not quite the best Trails game, but the best game of 2018, and a near-perfect conclusion to that particular story arc. My top ten for the year would be:

1. Trails of Cold Steel IV
2. Valkyria Chronicles 4
3. Monster Hunter World
4. God of War
5. Celeste
6. Super Smash Bros. Ultimate
7. Spider Man
8. Ni No Kuni II
9. Among Us
10. The Messenger

God of War was the very definition of the term EPIC! I couldn't believe what I was experiencing. Everything from the characters, storytelling, graphics, combat, music, boss fights was all turned up to 11 in a one a kind presentation. Loved every minute of it.

There were certainly some amazing games that closed out the year for me. Smash Bros Ultimate with a record setting roster and the Destiny 2: Forsaken expansion was practically a relaunch of the game! Up until I stopped playing, Last Wish raid and Shattered Throne dungeon were the best pieces of endgame content Destiny has had in the franchises history.

Some great games in 2018 like Celeste, Detroit Become Human and Spider-Man but I am once again voting;

“Other - Gris”

Monster Hunter World/Iceborne is one my favorite games ever, probably top10 ever material. I've sunk around 1000 hours into it. For my money its the best MH game ever made, and ive enjoyed it so much.

Another really great year with several amazing titles. God of War IV and SSBU are both worthy of the top spot but for now my vote goes to Ultimate even if God of War is probably closer to perfection since Ultimate does have its fair share of flaws. Anyways my top 5 for the year:

1. Super Smash Bros. Ultimate
2. God of War IV
3. Deltarune (Chapter 1)
4. Celeste
5. Marvel's Spider-Man

Spider-Man is amazing and would be the top of most years it could've released in, but Super Smash Bros. Ultimate gets my vote.

Battlefield V with Far Cry 5 as runner up.

Not a terrible year, not a great one either. I don't think there's any game I could vote in good conscience this year; no game seems worthy enough. There's definitely some fun there but nothing I'd really want to give such high praise, and even among the many games I haven't played, I just can't see any strong candidates. I'll abstain from voting this year.