Mass Update 2:
35. God of War III (PS3)
I enjoyed all the God of War games but this one was truly astounding. Some absolutely breathtaking moments with moving levels, over the top fights and the visceral combat that makes God of War so much fun.
34. Tomb Raider (PS1 & PC, also available on SAT, PSN) (remade as Anniverssary on PC, PS2, 360, Wii, PSP)
The original Tomb Raider spawned a new gaming icon, two Hollywood films, started numerous models careers and was a damn good game to boot. Nice puzzles, a wonderous adventure and at times frustrating difficulty (especially when judging jumps). The remake modernised the controls for modern audiences and retains much of what made the original a classic.
33. The Witcher (PC)
At a time when everyone was "dumbing-down" RPGs to appeal to the masses, along came relatively unknown CDProjekt with The Witcher that showed there was still a market for core/traditional RPGs. I've yet to play the sequel, but the original is one of the best examples of modern Western RPGs around (ignoring the weird sex card collections).
32. Final Fantasy VI (SNES, PS, also on GB Advance, PSN)
If you can't remember the SNES generation, you need to get and play this game. This truly is a showcase of the near perfection attained at the end of the 2D era. As far as JRPGs go, it's still one of the best around with a fantastic story and a diverse array of characters.
31. Metal Gear Solid 4 (PS3)
If you're a fan of Metal Gear Solid games, you'll love this. It beautifully rounds off the loose ends of the Metal Gear saga for Solid Snake. It does have a few too many cut scenes but has a deeply involved and emotional plot and classic yet modernised Metal Gear Solid gameplay (the first 2 chapters especially).
30. Counter-Strike/CS: Source (PC, other versions on X-box, XBL &PSN)
This is why PC gaming is great. A bunch of fans create a Half-Life mod that goes on to become one of the greatest multiplayer FPS ever. Through numerous iterations the game has kept improving and improving.
29. Call of Duty (PC, also on XBL, PSN)
The birth of one of the great gaming franchises in the world today. Call of Duty took the throne of WW2 shooter from Medal of Honor and never looked back. Great multiplayer gameplay and a superb single player campaign that saw you play as an American, British and Russian soldier, each giving a new perspective on the war. It's a far cry from the over-the-top action the series is now known for.