10. Prince of Persia: SoT - It had to go on the list because it's dialogue, story and atmosphere is among if not the best in the industry.
9. Ninja Gaiden Black - 3D action perfected.
8. Shadow of the Colossus - One of the most beautiful and evocative games I've seen and pushes the hardware in unimaginable ways.
7. Freespace 2 - One of the last space sims ever made and probably the best.
6. Metal Gear Solid 3 - Unlike 4, this was the perfect balance of gameplay and story, building up to one of the most amazing endings in gaming history.
5. Silent Hill 2 - If I tried explaining why it's so incredible this would break into td;dr territory. It's awesome.
4. Quake 3 - The most revolutionary and advanced 3D engine for years after it was released, as well as the most balanced and purest incarnation of old-school deathmatch.
3. Mario Galaxy - One of the most brilliantly fun and creative games ever, and easily the best 3D platformer of all time.
2. Half Life 2 - The most refined and polished fps ever made. Redefined the concept of physical interaction in gameplay, with some of the most amazing set pieces and scripting ever.
1. Resident Evil 4 - I've played through this game half a dozen times and it's still every bit as enjoyable. Amazing level design, pitch-perfect pacing, very lengthy playtime (but not so long that it wears out it's welcome), stunning art design, brilliant difficulty balancing and visuals that are eyecatching even today. I honestly cannot think of a single flaw. It's perfect.