The art is very stylized, not unlike the style developed for Batman: The Animated Series and carried over into the subsequent DC Comics-related animated series. (Which make sense, given that Wight is currently working on Batman Beyond.) The characters look pretty good, but generally speaking the female characters look better than the males. I think it's because he's not very good at drawing mouths. The creature designs are very nice, and his treatment of the Sunnydale HS library is gorgeous.
Thanks to animated-movies.com for the tip!