In no particular here is my top 10.
Unreal Tournament
I am sure this must have been the first FPS i ever played. Still a good game though and noticably the gameplay isn't really that much worse than modern FPS games. They havent really evolved in 10 years except bots, proper map editors have gone and health bars have been replaced with recharging 'shields.'
Star Wars Battlefront 2
I love this game the multiplayer is brilliant even though I never played it online just against bots. I never completed the single player though, I should go finish it now.
Super Mario Bros The Lost Levels
Not much different to Super Mario Bros but the harder levels, subtle gameplay changes (piranha plants & Hammer Bros act differently) and more sometimes weird levels (World 9 among others) make it a much better game IMO.
Digimon World
My first RPG. I am sure this must be the game I've played the most. It took me a few years to finish (needed a guide) and i still try and get some medals everynow and then. I am surprised this game was so good for a game based off a toy and TV series. It is also underrated and should be declared to have cult status.
Age of Empires 2
Love this game. It brought me into the world of RTS a genre I still love to this day. What I really loved about this game was the scenario editor and the cheats. Good times.
StarWars Galactic Battlegrounds
This game is basically just Age of Empires 2 but starwars-ified. Thats why I love it and because it makes improvements on AOE2 such as higher population cap and different factions units actually look different.
Gears of War 2
My favourite modern shooter. Brilliant Campaign, Brilliant multiplayer online and offline plus horde mode and a one of the few modern shooters with bots. Need I say more.
Saints Row 2
This game is pure fun. You can spray shit over people, phone a number to get a pimp to attack you plus any game where you can dress up as a clown/pirate/mime and control a small army (3) of ninjas has to be in my top 10.
Dead Rising
Love the wacky weapons. The showerhead being one of my faves. Can't wait for the sequel.
Fallout 3
If you reading this you, you must care why i put Fallout 3 on this list. Well I am gonna ask you this question, why wouldn't I put Fallout 3 on my top 10 fave game list.