#10 - Aliens VS. Predator 2 (2001) - A great shooter that came out even before the AVP movies. The game play was great incorporating the players ability to be either a Marine, Predator or Alien! Great!
#9 - Star Wars: Battlefront (2004) - Take any squad based war game and put it in the Star Wars universe and you have a great game. Battlefront 2 was even better by adding Jedi characters. Playing both rebel and Empire was great!
#8 - Marvel: Ultimate Alliance (2006) - This is a fun game especially for comic fans where you have a huge array of super-heroes to play with.
#7 - Spider-Man 2 (2002) - Even for a comic book movie tie-in game this was one of the best. The completely interactive New York City is fun by-itself as you web-sling your way through the Big Apple!
#6 - Grand Theft Auto III (2001) - This is probably THE most controversial game of the last decade, but it is still a fun experience, forget all the violence and the hookers, it's fun just to drive around in the city. Vice City goes hand in hand with this one too.
#5 - Resident Evil 4 (2005)- This redefined the Resident Evil series, which is still my favorite video game series ever since the first one! 2 is still my favorite but 4 brought Leon back and made him better.
#4 - Rock Band (2008)- Although I put "Guitar Hero" before this, it is still a fun music game and even better when you get friends together for the whole band!
#3 - Guitar Hero (2005)- This is still the best music rhythm game. I was a novice guitar player to begin with and I shamefully admit spending more hours playing this series than actually practicing my own electric guitar! The first was great, 2 was the best, 3 was good, but my favorite recently is Guitar Hero: Metallica! It rocks!
#2 - World of Warcraft (2004) - This is the best MMORPG of all time! I may not have been as engrossed in it as a lot of people and may have not leveled up as much, most of my playtime was spent just exploring the world! "For the Horde!"
#1 - HALO (2001) - This is the best first-person shooter ever! This changed everything. I spent a LOT of time playing multiplayer with friends and online. HALO 2 improved on the game play immensely and three was awesome. But I feel the first one deserves the #1 spot because it defined this decades gaming!