Favorite episode: Remedial Chaos Theory
Why?: It's the coolest episode of anything on TV, ever. As a Community episode with heart, it's good. As 22 minutes of format-defying entertainment, it's brilliant. 
Rest of the Top 5: Basic Rocket Science, Cooperative Calligraphy, Conspiracy Theories and Interior Design, The…

I'm not a huge Doctor Who fanatic, but I appreciated the references. It could have been better but it was funny enough and not atrocious TV by any means. I have no clue how it got a C-.