ah, i can see i'm not the only one who has posted several instead of just one.
my Favourite Videogame Of All Time was - without a doubt - Blacklight Retribution, before the developers butchered it in a manner so horrible that it should be recognized as "game that was most ruined by its own developers".
i have spent .. i don't know, five thousand hours, in this game? At some point i spent my entire waking day playing, i would play saturday until exhaustion, wake up on sunday and immediately start playing, and put in 10-hour days. Think the most assiduous MMORPG player, but for a shooter.
I played between 2012 and 2017 without rest .. i could have become a doctor, but not, i chose blacklight.
Also memorable for me was WipeOut 2097 (also known as WipeOut XL)
where i'm pretty sure i still hold a record (19.2 on Talon's Reach), depending if you accept only "as game intended" times or if you accept that sniveling french frog's out of bounds cheating times. (respekt)
A lot of games in the past were cool, like Wasteland, where i would just grind and grind and grind to have the most uber characters. This was back in the C64 years; i loved that game, but it was nowhere near as important to me as Wipeout or BLR.
there have been many other games i have loved, because i was young, because they caught my imagination (i.e. all the AD&D gold box games), because i played them with friends (Gran Turismo, Tekken 2 & 3, C&C95 - where i was a bloodthristy maniac and regularly won 1v3 games), or because the gameplay was so fun, like Lemmings, or even because the writing was amazing, like Day Of The Tentacle. But none have had such an impact on me as WO and BLR.