The art looks great to me, I like it a lot. It's just a different style, and that's a good thing. The only thing that needs work - and this should get better as the comic goes on - is the speech bubble layout. Some of them don't convey the conversations very well. But that's just a small thing.
I don't think it's even fair to compare it to OoTS in terms of artistic merrit: most of Rich's pannels give us a blank floor, a blank wall, and some mostly-pre-drawn character art. While the scenes in Erfworld are beautiful.
Now, I'll admit that when Rich puts his mind to it he can construct some impressive scenes (like Xykon's army, among others), especially when you consider that he can achieve these visuals without straying from his stick figure motif. Heck, the fact that he invented such a vibrant and bemusing style is very impressive. I'm not knocking the Giant's artistic skills.
But I do think that Erfworld is a much richer comic artisticly. Every pannel is a work of art in its own right; having mostly just stuck to Penny Arcade and OoTS before now, that's not something that I am used to, but I can still appreciate it. ^_^