Currently we have two episodes a lot of you guys consider lackluster: Putting Your Hoof Down and Owl's Well That Ends Well. The former because of LUDICROUS OOC moments from Fluttershy and the latter because the pacing is as interesting as watching glue toughen. Personally, I didn't find them too bad as a whole.
I myself was turned off by Feeling Pinkie Keen's religious undertones. For me, I found that to be a stupid move on the crew's part.
What're your personal worst episodes of Friendship is Magic?