I bought season 1 of Community on DVD as soon after finishing high school. I watched through it so many times. Really one of the most clever shows I've seen, full of all kinds of subtleties that'll go over your head depending on how closely you pay attention or just depending on how you view things.
I felt pretty disappointed with the second season of Community. I think it degenerated in the level of humour that was there in the first season. I put it down to Chang's and Pierce's change in roles. I did really like the episode 'Critical Film Studies' in which they do a play on My Dinner With Andre, though.
I haven't seen any of season 3 yet, but I'm sad that it's been put on hiatus (right?) seeing as how Community is still better than most TV shows out there.
A beloved scene from the first season: