The end of the Harmon era, and judging by the way it was structured, he had a good idea it was coming, from either cancellation or non-renewal of his contract. A smaller-scale episode — albeit one where Evil Abed runs amok and Troy becomes messiah to Greendale's air-conditioning repair school — that provided big emotional breakthroughs for Jeff, Abed, Troy, Britta, Pierce and Shirley, that concluded with the study group closer than ever, and with a season-ending musical montage like the ones "The Wire" always used. If you believe that "Community" ended with Harmon's exit, then this functions perfectly as a series finale. And if you're willing to give the new guys a try, it still offers a clean break between one era and the next, rather than ending on some kind of Sorkin-style cliffhanger that Port and Guarascio will have to clean up later.