Mmm, I don't like wackiness for the sake of wackiness. Never liked Ren and Stimpy for that reason.
'Course the opposite ain't so great either. Most animes are far too stiff in their character animation. Exceptions like One Piece generally have to justify it with in-universe reasons.
Guess it depends on what's being conveyed, as always.
Doesn't have to be wackiness. It's just nice when there is some justification to have used animation rather than live action. Miyazaki generally does a good job of this, not just with his strange creatures that would be difficult to do without CG (specifically the blob things) but also with his simultaneously majestic and quaint landscapes, probably best exemplified by Kiki's Delivery Service.
I personally don't think the character's are THAT well written in MLP, there's really no character development (It is a kids cartoon after all.) and people seem to flip their shit over little nerdy jokes here and there in a cartoon. Over all it's decent, it's just the small vocal minority of the fanbase I dislike.
Well, like you said, it's an episodic kid's show, so no it's not like The Brothers Karamazov. The reason they're well written is because they're three-dimensional. They all have believable flaws based on their personalities and though each has a most prominent character trait it isn't harped on to the point where there's nothing else about them (when handled by the better writers).
A question from the peanut gallery to the pony fans: I know that you guys say it's good, but would you say it's Animaniacs good?
Animaniacs? Yes. Freakazoid? Hm... They're really totally different though, it's hard to compare.