I'm a big fan of coop campaings, and Reach's was probably the dullest I've played in a long while:
1. No direction. Most of the time we just stood there like dumbasses trying to figure out where to go untill something lit up somewhere and showed us what the hell the objective was.
2. Horrible, skippable, cutscenes mean that in order to prevent one's sanity we just skipped everything, and realized that without them, the game had absolutely no story on it's own. I mean, the gameplay failed on every level to tell the player anything but "stay with yellow dots, kill red dots, go to the blue floaty square with a number under it". I mean, in the first three halos, even if you skipped the cutscenes, you knew what was going on. The flood is there, get the fsck out, soldier.
3. No flood. I don't care about continuity, no flood means no third act, no turning point, just plain routine. It also means that when the credit started to roll, we just shouted "wait, that's it?"
4. No real use of the new features. Reach's multiplayer is indeed brilliant, however with all the new tools (freaking jetpacks!) you barely get to do anything that requires their use, what about a mission where you must use the armor lockup at intervals to pass some security system or something, I mean, you could go through the whole campaign without touching the LB button once, it would have added quite a lot of variety. There was one level that for something like ten seconds required you to use the jetpacks, and that's it.
5. No mood changes, whatever you do, whoever you meet, they're gonna be there for a few seconds, then you get away and kill some more stuff, you never feel like you are in an actual city, civilians are cattle and other military types are there to give you their battle riffle before getting blasted by a stick grenade.
6. Frustrating vehicles segments. Space war sucked (lock on target, shoot missile, drift aimlessly until you figure out where the enemy are in the bloom filled sky, lock on, shoot missile, etc.) and that goddamn level with the chopper in the city was complete shit, directionless, pointless and not even really challenging.
7. Skippable last level? When the credits finished rolling I saw the animation of the spartans picking up his gun, with the skip button lit. We didn't want to go through another horrible cutscene, so we skipped to get right into the fight, and it just ended the game. I mean, what the hell?
8. The covenant is not a menace. By this time, after five single player Halo campaigns, we all know how to deal with every single enemy they throw at us. Big badass with shields and rocket luncher? Just get behind him and press b three times. Evil hidden sword guy? Shoot the bastard, then stick him and he's done. I mean, can we at least get a few new bad guys, something unnexpected somewhere or were they too lazy to create some new models?
9. Yay! Grenade luncher! Hey! Where is the ammo? Hey? Come on! Oh well, back to needler.
10. Okay, the hologram was damn cool.