Pretty good review. I haven't had a chance to play the campaign yet, but I was never a fan of any of the other Halo campaigns, so I'm not holding my breath on it. It sounds like it's really good though, so I'll hopefully get around to giving it a shot in co-op sometime soon.
As for the mutliplayer, it's been painful from the few hours I've got in of it so far. Three and four player split-screen Halo 2 and 3 were regular fixtures for a couple of years. The amount of time a few mates and I racked up on them just playing Slayer with random weapons and vehicles was ridiculous. Fast forward a few years spent playing Unreal Tournament, Modern Warfare etc, and Halo: Reach just seems so slow. That's not particularly bad, just different to what I'm used to now, and I'm sure I'll get used to it again, but it's looking like it'll take a while due to my true problem with the multiplayer.
The maps. Seriously, Halo 2 and 3 had some of the best maps I have ever played in a shooter. I didn't even have a 360 until about 3 months ago, yet I managed to rack up a godawful amount of time on a game I didn't even own. And yet, the only word to describe the maps I've played so far on Reach is "terrible". Maybe it's just me still struggling with the slower pace and not knowing the maps very well, but I just found them to be nowhere near as good as the ones from Halo 2 & 3 and MW/MW2.