Raze 2 in my opinion had better AI than Raze 3, which makes Raze 2 more challenging, and more enjoing, replayable.
Also about shooting mechanics. Raze 3 have fading bullets system, which makes bullets fade at the egde of the screen, or even on shorter distance. For example: assualt rifle's bullets can start fade just in front of the face of the enemy, which makes shooting sometimes anoying.