Thought I'd done mine already but obviously not...
1)
UO - needs no explanation, spent more hours on this than any game ever, years of my life sunk into it, got a quality group of mates from it.
2)
Final Fantasy 7 - every time I try and play an RPG of any sort, it gets compared to this and fails, the story and characters were just so good, and the music is awesome.
3)
Streets of Rage 1 - probably the first multiplayer/co-op game I ever played, played this with my brother for hours. the blaze esque bosses still give me nightmares with their jumping and heel-to-face fighting style
4)
Street Fighter Alpha 3 - in my mind the most balanced and clinical SF to date, it's hard to pick between this and SF2:CE though, as SF2 was the first I ever played and will always hold a special place in my heart. Alpha 3 was the source of loads of competition and banter with what are now my cardiff mates, but started off as work colleagues in the games store I worked at, and when we all moved away etc, we held tournies twice a year as an excuse to get back together and drink, play some sf etc.
5)
Legend of Zelda: Links Awakening - seems ridiculous to put this above Ocarina of time or link to the past, which are both amazing, but this was my first zelda game, my first real RPG/adventure game, and I loved its charm
6)
Sim City 2000 - this is the game which got me addicted to 'god sim/builder' type games, and I just loved its simplicity and freedom. It was a tossup between this and the original populous for this spot/genre
7)
Aliens vs Predator - my first go at competitive multiplayer gaming (one of the few games except uo I wasn't shit at). Played this with a group of mates I was in high school with and fucking loved it, really well balanced despite lots of cheats, and experienced my first taste of online rivalries with what must have been other 16 year old ego-heads, was also the cause of my first ever giant phone bill..
8 )
Phantasy Star Online - First co-op game I ever played online, with some mates I was working with at the time. I just couldn't get my head around it, all the little sega homages and intricacies, cool weapons, character customisation, trading etc.
9)
Dizzy the egg, c64 - one of the first games I ever played in fact, and just weirdly charming. I remember I spent my birthday money on a joystick just so I could play this better (after spending about 8 minutes loading it from cassette of course!!)
10)
Halo - I remember when I first played this game, when xbox was released. Completely groundbreaking, amazing story, AI, controls, great multiplayer and co-op and just seemed so polished at the time. Played this again recently and whilst it is obviously dated compared to what we have now, it still seemed pretty solid. I think I also associate this with the time I started working in a videogame store (same week xbox was released) and it was just a cool time to see how excited people got about games, when I thought it was just me!