Halo 1 - great gameplay, simple plot, balanced and challenging difficulty, high replayability due to level design, AI, and freedom. Has a decent port on the PC, lots of modding support, Custom Edition, and there's a lot to love about the animations and sounds. Subtle glitches, you can use level skips to make a battle play out differently. The only thing I didn't like is 'Press X to enter a vehicle'. I felt like I was the Master Chief. Halo 2 - utter disappointment when played as the developers intended. Glitches, easter eggs, and skulls make up for it's gameplay, but barely. The AI are less convincing. Exploration isn't that great in scope; only Delta Halo comes to my mind with it's level top. Replayability is hindered by inconveniences like checkpoints lasting only 8 seconds. Any difficulty above Easy can be overwhelming and hinder approach. Interesting plot though. I love making an Elite army (as in my sig). The Arbiter is a cool character and playing as him is more preferable to the Master Chief. [Edited on 10.18.2012 5:04 PM PDT]