Looking back at this thread, it looks I didn't post a serious answer.
So that is either Grand Theft Auto 3 or Metal Gear Solid. Both games blew my mind when I first played them.
OG Final Fantasy VII was a great experience, and also Ocarina of Time… I wouldn't say either of those games hold up particularly well by today's standards though (FF7 perhaps slightly better).
I think I'd have to go with Sekiro though. Just a wonderful and immaculate experience, and my first flirtation with FromSoftware. Punishing at times, but I still don't think I've hit a 'gaming high' on the same level as beating Lady Butterfly and then realising I could actually get through the rest of the game ha
The Witcher 3 or Mass Effect 1. Love 'em both to bits.
If I had to pick one, it would be Resident Evil 4.
Crikey — favourite game of all time! Narrowing it down to one is gonna be tough, but contenders for me would be: Mafia 2, Red Dead Redemption, Metropolis Street Racer, Shadow Of The Colossus, Horizon Zero Dawn, Far Cry 5, Grid Autosport, to name a few — bit I'm gonna go with the game that effectively kickstarted a whole different period in my life, affecting my interests, life choices and ultimately leading to me finding my partner...
… and whilst not necessarily a great 'game', its the experience and legacy that this game brought to my life, which no other game has really matched.
My choice: Shenmue on Dreamcast
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