The art is really just okay. I have the DVD version and thats all i can say for it. Rather, I think Air and Five centimeter has more of a storyline to it. I think the only reason i can compare Five centimeter with Renmei is because of the "leaving friends behind" feeling they both have, Air is just plain depressing despite its awesome graphics.
However, if you look at the art as something important, I really suggest
Serei no Moribito.
I'm really jealous of you, Samurai Champloo rocks!