It was a negative experience for me, still is, and now more than ever.

I came from LAN multiplayer which is vastly superior to online multiplayer. No lag, in the same space with friends. I started LAN gaming with Duke Nukem 3D and carried on until UT2004. So many great memories, so much fun! Just as good as couch co-op.

The rise in online gaming took all that fun away. No more effort to come together, rather play online with often shitty voice sound quality. When I got older friends didn't have the time anymore to play at the same time so you end up with random people, which is 100x worse experience.

My days of Everquest were so addictive since we combined LAN with online play. I was playing side by side with my fiancee, together playing Everquest and later WoW until we didn't have time for that anymore (kids arrived)

Anyway in the end the rise of online has brought more negative things (eternal patches, monetization, always online, decline in couch co-op games) than positive. I rarely game online anymore. I recently tried again with GT7 and it ended up confirming why I don't do that anymore. Lot of waiting, assholes online, disconnects, dealing with lag.

Online gaming is mostly a negative experience for me.

I didn't feel the step from 2D to 3D that much since there were already plenty 3D games from the start on PC with vector graphics. By the time Wolfenstein 3D came along with textures, I had already played tons of 3D games, including 3D Pacman, 3D Tetris, racing games, flight games. Also on MSX, some real 3D with vector graphics and sprites, some faked like Outrun.

Adding textures to 3D was a huge step though, yet so was adding textures to 2D games. 2D games are still popular as well. A real transition is from B&W to color TV. The only times you see B&W nowadays is for some art project. 3D and 2D gaming still happily co-exist, same and on and offline games. Still big step fowards, but not quite transitional.

Transitional would be the standardization of the controller and controls in general. Perhaps dual analog sticks is a good one for the 21st century. That opened up a lot of new game play possibilities and quickly became the standard.

I too was thinking dual analog sticks but that was introduced in the 20th century 

True. It didn't really become standard straight away though. At least not how they are used today. But yes, 1997 was the first twin stick controller. 1999 Ape Escape the first game to require use of both sticks. (Although the right stick was only to select actions, not used analog)

Alien Resurrection (October 2000) was the first FPS to use dual analog sticks as we do today.

Anyway dual analog was transitional. The d-pad is now used for actions rather than movement.

You know I decided I am going to change my answer. The correct answer is Steam. By far and away the largest gaming service with the most gamers, widest selection of games.

When people say online and how it counts because of much better it became, my mind keeps defaulting back to the massive leap off a cliff in online functionality and freedom from Bnet 1.0 (1990s) to Bnet 2.0 (2010s). Just my personal experience, but online gaming in 90s (and then into the 00s) on PC was awesome.

The answer above me is a good one (Steam). Surprised no one's mentioned support for, and the move to, HD resolutions on the console side of things.

Apex is there. Morphies Law is there. Is Ninjala a shooter? I don't remember anything about it. Also indie games with online modes. I'm sure the goal post will change again because it's not CoD or whatever.

Nope. 1989 for SEGA Mega Drive is the first Twin Stick analog controller.

Oh cool. That's more a precursor to Hotas though. Right stick can clearly only travel up and down.

Wild controller! I never had Sega until Dreamcast.

Steam completely changed how games are delivered on PC, very valid answer.

Sadly it also turned Valve into a store keeper instead of making games :/

Wrong as usual.

Just ignore Zeldaring, he isn't offering anything factual to discuss.

This.
We went from having to hunt around for CD's and CD Jewel cases to input CD Key's to a full digital system.

Valve did start to branch out into hardware though with Steam Machines, VR and now Steamdeck.

The PC was a good 10 years ahead of the consoles on this front.

Overwatch was another popular one.

Lots of shooters on Switch with decent populations.

Yeah, split screen is basically a thing of the past these days... Which is unfortunate as it was probably where I had the most fun as a kid... Nothing beats 4-way split screen Goldeneye/Perfect Dark for hours on end back in the 90's.

I was playing the original Age of Empires on zone.com back in 1997 on a 33.6kbps dial-up connection, I thought it was incredible.
...But we still had to use things like MSN messenger to organize groups and such, now it's all seamless and integrated and feature-full... So when original Xbox gamers started touting online gaming... It was a "welcome to the club" moment.
Sony and Nintendo eventually caught up and now it's just a standard expectation.

The impact to HD was probably less for me as a PC gamer... As every few years I just had a bump in resolution anyway so I didn't really notice the jump to HD.

For example... 640x480 on the Voodoo 2, 800x600 on the Geforce 256, 1024x768 on the Geforce 3, 1280x1024 on the Radeon 9700Pro and so on, if anything resolutions have stalled at around 4k, with the optimal resolution being 2560x1440 with higher refresh rates.