First half of the episode was ok. Highlights were Maggie doing the nazi salute, spoof of the social network ending, Marge calling Homer "Ralph", "Fred" and "King Of Queens" , "What about mimes?" "I'm not made of stone", and young springfieldians in the flashback.
Then it got really dull and boring, and Joan Rivers character got annoying and finally it ends without a decent conclusion. I did like "I love everything about the past except the way it leads to the present" and the coach gag was really, really clever and funny for once (and short).
I also liked Krusty's best review ever, though they maybe make him a little too much of a loser in the recent days. They used to make him more succesful, even though he's kind of a terrible person since Bart The Fink or even earlier, but I guess that if he got some famous he should have got good reviews sometimes. Or maybe it's just the audience who likes him and not the critics.
Anyway, it started ok but it was dull for the most part and it lacked a good ending. A very mediocre episode. 3/5, being generous.