Well this has certainly been a night. Adventure Time was not only awesome, satisfying, refreshing, and progressive, but Regular Show literally bombed us with that little "Margaret going to college" thing. I can't say I'm disappointed: both shows have moved us forward to more critical points in the series...
Finn is finally growing up (or down, depending on how you see it). He is realizing his big mistakes and coming to some important crossroads. He is maturing enough to try and win back Flame Princess, but also seems to be getting completely over PB. At the same time, he isn't ready to assume adult responsibilities which is both a relief and a disappointment. Do you want Finn to grow up or stay young? The episode left the meaning to both sayings ambiguous. (As an aside, PB was also very cool in the episode).
Whether Finn is benefitting from this change in perspective is for you to decide.
Mordecai is finally together with Margaret and is about to finally go steady with her when she gets accepted to her dream college. Now Mordecai has to let her go because he does love her. This signals Margaret's temporary departure from the show. Winning Margaret's heart was a central plot element to the show almost since the beginning. Seeing her go is bitter-sweet: on one hand we hate to see Mordecai lose the girl who might be "the one". But on the other hand, this assures The Regular Show is going to have a renewed lifespan. Finally putting Margaret and Mordy together isn't necessarily "jumping the shark", but it would be concluding a huge conflict. I think the writers made the right decision on this one. Now our boy is gonna try twice as hard to win her back, but the fun can still go on.
I know this is AT, but I thought because these two bombshells were dropped on us, it was just too big to ignore. Now we can talk and cope together. I wouldnt normally do this, but today it just seems right. What a night. Well done, AT and RS.