* This borders on being an ungrateful shit, because Infinity Ward took the time to add co-op, but why was Spec Ops designed for only two players? These days, I can only justify two-player co-op if it's the actual story mode. But since Spec Ops was designed specifically for co-op, this is a very odd decision. Between Gears of War 2, Halo: ODST, and both Left 4 Deads, I don't see Spec Ops having much staying power.
* Love the new heartbeat sensor, which acts exactly like the motion tracker in Aliens. In other words, you know that someone is close by, but no idea if they are above or below you. For me, this device is a perfect fit, because it has greatly decreased the times I've been shot in the back and, more importantly, it's provided me with countless opportunities to legitimately quote Bill Paxton's character in Aliens.
Best instance: inside a two-story office in multiplayer one night. A red blip showed up on the heartbeat sensor mounted to my gun, which appeared to be only a few feet away from me. With the thought that I'm terribly clever in my head, I said to my very unimpressed wife in my best/worst Bill Paxton voice: "But that's in the room, man!" Seconds later, I turned around to spot the red blip in person, on a balcony above me, who had spotted me at almost the same time...but since he had a few seconds advantage, he got the drop on me. In real life, I let out a yelp of surprise. My avatar died quite painfully.
The wife, it must be said, remained both unimpressed and uninterested through this serious of events.