Had a firefight on the moon earlier that made Halo look like junk. The AI is scary good at times. They rush, they flank, they circle you and come back when you're hurting.
It has the pure refined DNA of Halo in the minute to minute gameplay.
It just doesn't feel that way for me. The minute-to-minute gameplay for me boils down to "shoot a guy in the head until my clip is empty, take cover and reload, then go scrounge for more universal ammo packs because I'm already low". If the enemies are really giving me a hard time, it just means spending lots of time waiting in cover while my shields recharge or running a relay race between the few viable cover points.