Loved the first episode. I actually felt that the voices were all pretty spot on. My only concern for Medaka's voice in particular is when it gets to the more serious arcs, whether or not her seiyuu can handle the darker personas. I mean I'm sure she can, or else she wouldn't have gotten hired. Anyway, it's good to see Gainax doing a good job on this. And to whoever thought they overdid it on the ecchi, this was actually pretty much completely on par with the manga for this chapter. The only difference is that since it's animated, they had to spend more total time looking at the ecchi frames.
DEFINITELY looking forward to next week's episode, looks like they're gonna speed up through the next chapters to get to the new character intros.