For me, Season 2 was possibly the best sophomore season of any show. No sophomore slump.
Seasons 1 and 3 are about at the same level for me. Highs and lows. When it's on, it's AMAZING; and when it's off... it's still much better than most crap on air.
Time Magazine's analysis of the show is very accurate:
Community is television's first Cubist sitcom. Like the still lifes of Picasso or Braque, it starts with a simple tableau: a set of friends/acquaintances/nemeses in a community-college study group. Then, episode by episode — like a painter breaking a guitar into geometric shapes — obsessive creator Dan Harmon rearranges its component parts to play with perspective and create a picture truer than real life. One week the story is built around seven alternative timelines. Another, it's a parody of My Dinner with Andre. Another, it's told entirely through flashbacks to Community episodes that were never made. It's not just invention for its own sake but a way of using the storytelling frame to show how each character in the ensemble relates to the whole. Yet Community is not some high-art experiment but hilarious, good-time entertainment; it both defies sitcom formulas and lovingly embraces them. Unfortunately, NBC has just placed the low-rated series on hiatus. It should return later next year, and it may yet be renewed. If not, what we've gotten is worth hanging in a museum.