I absolutely LOVE that perspective. It's a very clever way to put equal focus on a small creature when she's standing next to (er, on) a much larger animal. And, of course, the characters themselves look fantastic in that semi-angular style. The rat especially... those little brats are surprisingly difficult to draw, and your anatomy is spot-on.
I'm also stoked that there is a t-shirt version... can't wait to get it in the mail!