For adult games? Definitely Midlife Crisis. I was such a fan of that game; I replay it often. Shame the creator vanished awhile back; hope they're doing alright.
Non adult? Elder Scrolls I have sunk a lot of time into the various games. Same with Mass Effect.
For adult games, Lessons In Love. I had originally planned to do a full review thing on the game so I replayed it several times and got stuck doing in depth analysis for so much in the game while also playing new content. The game just felt like it had phenomenal writing.
Mainstream: Skyrim
Porn Game: Skyrim with lots of mods
* I slowly modded skyrim to be a pregnancy simulator with combat and bondage and brothels for my offspring
Most Pokemon games since I like to shiny hunt. Probably got at least a few thousand hours combined.
Skyrim probably has like 500 hours cause I keep modding it and never actually beating it lol.
Elden Ring is about 300 hours right now. On my 6th playthrough right now as a randomized co-op run.
Maplestory, especially when I was younger. I don't even want to think of how many hours I put into that one. It wouldn't surprise me if that one was in the thousands.