1. Zelda Ocarina of Time
2. Doom 1/2 (this is what got me into PC gaming)
3. Wolfenstein: Enemy Territory (this is what got me into multiplayer gaming and it's still awesome)
4. Half-Life 2 (this reinforced my love for PC gaming)
5. World of Warcraft (take that as you will, this is the first MMO I've ever played and although I don't play it anymore, I just can't dismiss it)
There are other amazing games that I consider some of the best I've ever played.
Honorable mention goes to:
*Metal Gear Solid (up there in my top 5, along with Ocarina of Time)
*Silent Hill 2 (I think that any person that loves SH2 knows why everyone else loves it)
*Resident Evil 2 (The first game was crap, there, I said it, but the second was much more scary, longer and a bit less silly)
*Fallout 3 (I've played Oblivion before and I liked it, but Fallout 3 was simply better)
*Borderlands (Diablo who?)
*Metroid Prime (I never thought that any game could top Super Metroid, I was wrong)
*Eternal Darkness (By today's standards, this game isn't even scary anymore, but it still holds an amazing story)
*Team Fortress 2 (although I never played it that much, you've got to admit the impact it has made in the industry)
*Guild Wars (yup, you can't jump; yup, you can't swim; yup, you can't hold more than 8 skills at a time, but still this is an amazing game overall and I loved it's difficulty, it actually made me think before acting)
And many, many more I may forgot about, but I still enjoyed a lot, but I'm just too lazy to name them all.