One of my first downloads for iPad and our 3+ daughter loves it. She dived right into drawing with the various tools, having no trouble switching between tools and colors. She creates new drawings in minutes and loves to save them and review her former creations.
Issues: It took me a little while to figure out how to save (click the "USB cable" tool, then the album) and longer to teach the toddler how to do it herself - ideally the drawing would "autosave" itself so that drawings would not be lost. Going back and forth between the current drawing and older drawings and saving/updating drawings should be easier. That said, we are managing with the current slightly awkward interface, and it is her favorite iPad activity right now.
Separately, the tool drawer interaction is a bit awkward. Ideally, it would hide/reveal itself according to safe gestures, but as it is, I often find myself marking the drawing accidentally as I try to make the drawer open/close.