A game that's just there.
A gravity hammer wielding brute was the only real challenge and even then only if I got cornered. Even the flood were a joke. All I had to do was run through or around them occasionally rifle whipping one who jumped in my path and that was it. And how **** was the gravemind? I fully expected and hoped to fight Cpt. Necro towards the end of the game but again I was disappointed. All he did was get all hot and heavy in my ear while I trudged through it's bowels.
The story dynamic, which was a major driving force in the previous games, was superficial, poorly executed and disjointed this go round. And the ending left so many loose ends you could trip and strangle yourself with them.
Halo 3s saving grace is its online play and the detachable camera in the film menu. Which, when I think about it, is what it seems Bungie spent most of it's creative effort on. Unless your making a game like Warhawk that's exclusively an online experience, then a solid campaign is a requirement. Halo 3 stands on shaky legs at best in this regard and more or less comes off as a game that's just there.
But what do I know. I'm in the minority on this subject it seems so I'll just shut up and go play Bioshock again.