This is a difficult one, because as time went by my favourites changed and I also had favourites in different genres.
When I started gaming in the early 1990s, Duke Nukem (2D)/Bio Menace/Commander Keen were my favourites and remained that way until Need for Speed II: SE, which took way too much of my time for the next few years. After that, Age of Empires was good but Age of Empires II was what really grabbed me. Between all this I had others, such as Tomb Raider III and Quake III Arena. I was a young kid at the time, so there were some educational games in the mix as well such as The Magic School Bus.
In a nutshell, these are the games that did it for me:
Need for Speed 2: SE
Tomb Raider III
Future Cop LAPD
Suzuki Alstair Extreme Racing
Age of Empires II
Quake III Arena
Add to that there were games I was too young to fully appreciate at the time which are brilliant, such as the Monkey Island games, Grim Fandango and Dungeon Keeper.
From the 2000s onwards there have been many games I've thoroughly enjoyed but don't belong on this list, such as Bulletstorm, Age of Empires III (which I still play regularly), Battlefield 3, etc etc etc.
OP, your question isn't quite as straightforward as it first appears 😁
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