Seasons 1-3 are perfect TV, imo. Season 4 is decent but feels like someone trying to do an impression of Community rather than the real thing (which, you know, writer changes always cause that). Season 5 is super, almost back to the quality of 1-3 but doesn't quite manage it. Season 6 is weaker than 5 but stronger than 4.
Always watchable, always charming, almost always hilarious. Watched it for the first time when season 3 ended and fell in love with it almost instantly. I was only 17 so it's informed a lot of how I watch TV and look at the world, to be honest. Have seen every episode several times. Glad it's getting a bit of a resurgence.