South Park has been getting worse and worse, starting with the 7th season. Season 8 and 9 are just bad. SP used to be random madness with some social commentary humor thrown into it but recently they just pick one issue, make an episode out of it and everything just revolves around that issue.
SP is going the way of MAD magazine. MAD was funny when they had Don Martin and Spy vs Spy and all that stuff that didn't make much sense but was genuinly funny. Then they turned to movie spoofs and parody of current events and the whole thing turned shit.
I didn't think the Mormon episode was particularly good but it was watchable. Sadly, it was one of the better episodes of that season. The Scientology episode had a lot of promise but in the end it was disappointing.
These more recent South Park episodes are too much about topic of the episode and neglect what makes South Park funny.
When I look at my favourite episode list there is barely any Season 8 and 9 in it. I'd probably rate only "Woodland Critter Christmas" as a classic.
Just compare the Mormon and Scientology episodes to the double episode in which Cartman founds his own fundie Christian church ("Do the Handicapped go to Hell?" and "Probably") and you'll see what I mean. Or Jewbilee.
They've run out of ideas. There are plenty of topics for them to makes episodes about but these episodes lack any creativity and are too narrowly focused on their "message" or whatever you want to call it.