The spawning can be very annoying, especially in Deathmatch. Then again, Deathmatch maps being as small as they are, I also understand there's not a lot they can do about that, short of spawning people on rooftops. Now it is true, though, that I get spawned in front of my pursuers in Manhunt way more often than in Brotherhood.
As for the contested kills, I'm all for them, I think they added something nice to the game there that, I'll be fair, can be a source of frustration if you see your carefully built-up Incognito go to waste. But that's part of the charm. And on the flip-side: nice source of extra points for dying.
And roofing, well, roofing is running rampant in Simple Deathmatch, which is why I don't like to play a lot of that mode. But in all honesty, roofing is probably a very valid strategy, especially in Simple Deathmatch.