Well, as CMC episodes go, "One Bad Apple" is not as great as "Hearts and Hooves Day," but definitely better than "Family Appreciation Day."
As always, the voice actresses for the three Crusaders do a great job!
The song was quite enjoyable, with fun animation going with a fun song.
I also loved the A-team-like music during the construction sequence. Nice touch.
The parade sequence had some great humor with Pinkie Pie (naturally). VEGGIE SALAD!! :P The initiation sequence with Sweetie Belle's reading and Scootaloo's drumming was quite funny too.
As far as the overall episode, it wasn't terrible, but it wasn't quite up to the level of the first three episodes of the season. I give it a B.