1. Super Mario 64
See my review for my thoughts but honestly this one is amazing.
2. World of Warcraft
Very different game to SM64 but it is arguably the first Massively Multiplayer Game to also be a good game.
It is not perfect but it is the very best example of a very specific type of game.
A type of game that I hope is moved away from in future MMO releases since I don't need another game that play a lot like WoW when I have WoW.
3. Tekken 2
This has a special place for me. I lost many an hour to this little number as a little un. The characters their expansive library of moves intrigued me in my youth, I would get to energised playing this game that I'd be jumping around my friends house for hours after every play session imitating all the moves.
Heihachi's electric noogie was pure class, LOVE it!
4. Pokémon Red/Blue
Not in concept so much as reality this was my first RPG. I learnt to love levelling up and using Water to beat Fire and beating Ice with Fire somehow (frozen water is apparently nothing like normal water, apparently).
The RPG systems that underpin Pokémon are sophisticated than nearly all Final Fantasy and Dragon Quest titles and the number of things to do in each title is truly staggering and makes a fool of any game that attempts to compete.
I love Pokémon and I always will I suspect, much like kids of older generations still love G.I. Joe in their adult lives I will still hold a candle for Charmander and a umm leaf for Bulbasaur!
5. Sonic the Hedgehog
I love Sonic. I payed my own money to play the 2006 game of the same name and completed it. Even thought I knew that it was in no way a good game a still pulled every tiny bit of fun I could out of that game because I wanted a current generation Sonic title so much that I would make a the most of a terrible lot.
Sonic Team have got completely nuts for the record but I digress.
This game and it's sequels are some of the first games I played as a tyke (I think Sonic 1 might even be the first console game I ever played at the age of about 3 although I might have played something before and just not remember that far back) and I love 'em. I even got the Sonic the Comic and collected it for ages as a kid, I only stopped buying them as they started mostly just reprinting old stories and crappy new short stuff.
Playing this for the first time was a real moment in my life, it is a big part of be being the person I am today, the men that worked on this game crafted my childhood memories, their imagination will be with me forever.