Just finished on Veteran. About seven and a half hours all told. I guess that's a touch short, but I only ran into a couple places where I got bogged down and they weren't anywhere near as bad as Call of Duty 4. I'm more than happy to spend seven and a half and not be frustrated rather than spend ten or eleven.
Quality wise, this is a high bar for action games/first person shooters and I don't see how Bad Company 2/GRAW 3/etc. are going to come close. I had huge concerns regarding the story based on spoilers I had seen, but ultimately I completely changed my view. (And no, it wasn't hard to follow - a problem I've had in the past with this series).
But the way this story is presented, both directly to the player and on the surface, is excellent. The themes presented are plain as day, they're pounded into you and it's very, very effective. theignoramus touched on that and he's absolutely right.
Gameplay-wise it's more of the same, refined. The set pieces are great, the variation in pace and style is quite good, etc. If you have a good time playing Infinity Ward's campaigns, you're going to enjoy this. There's nothing terribly innovative as far as gameplay is concerned, though.
And for the final time, there are no more infinitely respawning enemies. Tough spawns and crackshot AI, of course. But they absolutely, without a doubt in my mind, do not infinitely respawn.