I've taken two adult beginner ballet classes at Martha Hicks School of Ballet, one with Martha, and another with Tanya. Both were great - Martha's class was more focused on mastery of technique, and she really took the time to correct posture and by the end of it my calves and hips were burning like they'd never burned before! Tanya's was a bit more advanced but relaxed - she strung a few basic moves together - and it seems like the class is more for the enjoyment of dance/movement.
The other two things I love - the classes are also reasonably priced ($13 for drop-in, $120 for a 10 pass) compared to other studios further downtown with excellent teachers - and also have live pianists, which I find really is fantastic compared to songs played off an iPod!
The only thing that is a little off-putting is that there are a lot of teenage girls there at the same time, so changing facilities can get crowded.... and like you're on the set of Mean Girls.
Otherwise, awesome! I will definitely be back.