1. Brothers: A Tale of Two Sons
I've never played a game that had me so immersed in the world and in the story of the characters. This is only enhanced by the control scheme that truly makes you feel as though you are the two brothers. It does all of this without a single word of any real language being spoken.
2. Portal
This was the first and only game I have ever considered perfect. The gameplay was unique and complex, the story is deep and rich, the world perfectly displays the themes of the game, the voice acting was sublime, the level design was unparalleled etc. etc. etc.
3. Shadow of the Colossus
This is the closest thing to perfect outside of Portal. I am a big critic of the tone of games, how sometimes there is a large disparity between the overall message of the game and the messages being displayed in certain aspects. This game stays true to it's source material, stays true to it's excellent writing and delivers the second most emotionally responsive game I've ever played behind Brothers.
4. Team Fortress 2
This is a bit outside of the box, but I have had more fun in this game than any other that I've ever played. I've played thousands of hours of this game between Xbox and PC (Yeah, someone actually enjoyed the console version). I could log on right now and find out something new about the game within the first five minutes. Whether that is playing a new game mode, a new map, or something else through the beauty that is the Steam Workshop. It is still better than any FPS I've ever played and will stay that way for a long long time.
5. Psychonauts
I adore everything about this game. Tim Schafer is better at designing characters than any other developer out there. The man is a genius. It is a hilarious game where each character has their time to shine. However, they do this without over saturating the game with characters that you begin to like and then they are gone. This is something I am eternally grateful for and will love Tim Schafer forever for.
6. Just Cause 2
Take everything I said about Team Fortress 2 and add a remarkable grappling hook to it. This is as fun as any game I've ever played and it falls behind numbers 4 and 5 in my list simply because I do not care for the story and the characters as much, which is weird because I am much more of a mechanically oriented gamer typically.
7. Pokemon Emerald
This is, in my opinion the best of the Pokemon games. Although I was an expert in the Pokemon scene before this game came along and didn't deviate from its predecessors I still found myself replaying this over and over again for years. I love all Pokemon games (save generation 5) but none of them captured me the way this one did. I have no real explanation for this, it just did.
8. Spiderman 2
This is undoubtedly the best movie tie in game that I've ever played. It stays true to it's source material whilst still having it's own creativity. It had the best and most fun way of travelling around in a game I've ever played with its web swinging. It's not as immersive as the other games I listed, but this is where my preference towards solid mechanics comes through.
9. Ocarina of Time
We've all played this, you know why it's here.
10. Sonic 3
This is a sentimental pick to me, it was the first game I ever played and it immediately got me hooked into gaming and I haven't turned back since. This is still the best Sonic game to this day other than fan made versions of the classic Sonics.
Also, this little hedgehog is far superior to that fat plumber guy in every way imaginable. Except Sonic 06, which we don't talk about.