I picked up my copy today.
I've played single player for about an hour now, and it's definitely very good. It's going to take some getting used to finding health packs to get your health back though.
Also ammo seems to be in short supply so there's not going to be much firing in the general direction of the enemy hoping to get in hits.
I'm looking forward to trying out the firefight mode. Which I think is GoW2s horde mode Halofied...
One of my firends beat the solo campaign in under 5 hours on Insane. I don't think I'll be doing that, I'm having trouble on normal, but that's more to do with the fact that I'm aiming using a control pad and not the PC.