Jams are tight on time and hopefully full on learning. I've yet to complete one where I haven't had a list of things to improve on. It's also easy to be an 'ideas guy' for someone else's project because proposing ideas is easy when you don't have to implement them. The fact that you want to continue working on it afterward is great! and even if not on this game, there's always the next project or jam.
For drawing and the rolling animation, I thought the sprites you did have were good. Subtle motions can get a lot across, even just a sprite with the head tilted down would help, and the rotating sprite will cover for a lot. Otherwise, improvement is practice and repetition. But don't just practice with pandas to draw pandas, how something looks and moves compares against how it looks and moves differently from everything else.