Portal 2
Duke Nukem 3d
Amnesia: The Dark Decent, Cyberpunk 2077, Deus Ex: Human Revolution, Factorio, Dark Souls 1
Overwatch or RDR2
Stardew Valley
Crazy Machines 1.
Borderlands, specifically the original release on xbox360 with all 4 DLCs. Off and on I've probably spent over 1000 hours on it over the past decade.
Changes from time to time. Overall the best game I've ever played would probably be DayZ but the game I've put the highest amount of hours into would be either Runescape or GTA San Andreas Multiplayer (SA-MP)
TF2.
Slay the Spire, Cataclysm: Dark Days Ahead, TF2, Wolfenstein Enemy Territory, Morrowind to name five going backwards in time a little. I've been playing computer games since text adventures were the mainstay though( got my TRS 80 model 1 in the late 70's) so there are a ton I have to leave out. The NES was probably the greatest thing to ever happen to me as a kid though and all the games that you'd expect are up there on my list. Having a Super Mario Bros. at home that was almost exactly like the arcade machine was a freaking REVELATION. Soothed the wounds of PacMan on Atari/Colecovision that had been open for a long time.
Pokémon Colosseum and Majora's Mask.
Tough one, but if I based it on what game I've replayed from start to finish the most times, Symphony of the Night. This is significant because I rarely replay entire games.
Probably rocket league. Other favorites are Civ 6, Balatro, Monster Hunter Franchise, and the Dark Souls Franchise.
Back in the day it was Sim City 4 and Age of Mythology.
