My review:
Carnival - Awesome setting, very balanced, somewhat a camping map, but a huge number of ways through the various chokepoints and counter camping spots. I like it, a lot.
Fuel - As advertised, it is quite large. Pretty good map, could do without the wide open portion on one side of the map, but still enjoyable.
Trailer Park - Run and gun map, pretty cool, shotgun heaven or hell, depending on which side of it you're on. Overall seems good though.
Strike - Didn't really like it in COD4 (dependent on game mode) and really, honestly, still don't care for it (dependent on game mode), it does look prettier though, which is more than we can say about the Stim Pack map remakes.
Vacant - Same old Vacant you know and love sans one change where they previously had a doorway blocked, it now is open. It looks a lot better, though.
I'd say its worth the $15 if you plan to play the game a lot, if you plan to play casually, wait for a sale on MS points or something obviously.