Well, I finished Season 4 a few days ago.
I immediately started enjoying it just as much as any well-written cartoon. The characters are a large cut above some of the crap that turns up on television, and there are some definite character developments throughout the series (not all of which I particularly liked). Discord has to be among my favorite characters in the show, his voice actor is phenomenal at making Discord interesting, funny, and really likeable. And another notable character whose voice I immediately noticed as soon as he started singing was Cheese Sandwich voice by Weird Al, which was a really cool and unexpected surprise.
By the end of the first season I felt like I knew our main 6 characters very well. My favorite in order from most to least favorite up to the 2nd season are as follows : Fluttershy, Rarity, Pinkie Pie, Apple Jack, Twilight Sparkle, Rainbow Dash.
Oddly enough, I imagine due to the change in writers, there was a pretty massive shift in how much I liked the characters after season 2, my list then changed to : Fluttershy, Pinkie Pie, Rainbow Dash, Twilight Sparkle, Rarity, and Apple Jack.
All in all, I really enjoyed MLP and I'm really glad that I decided to give it a go. And honestly, I feel like less kids would grow up to be assholes if they watched MLP.