Having put more time into the MP, I'm liking it more now. This could be because I'm getting better at reading the levels, but they've settled into something more resembling CoD4 than I originally thought a few weeks ago. There's more people running around, generally less camping, etc.
I do think some levels are still pretty bad, in the sense that a game can become lopsided in seconds. Estate and the one with the central bunker surrounded by a wide open field come to mind, since it's difficult to get a beat on where you are safe. Favela does this a bit as well, since it's more attuned to vertical play than anything.
But I'm having a lot of fun, and think it's very well made. I'd love to see an option to get the CoD4 maps, and then set up an option where you play only those. Of course this might happen as buyable DLC, which would be somewhat annoying, in that I'd totally buy it.