Thanks for trying out my game! I tried to add at least something new for most levels, so the game wouldn't feel stale — adding new Pengs didn't take too long, since they all use the same basic model, but adding new enemies did take some crunch time. The polar bear was originally going to be the final boss, but I had some extra time after making its level, so I decided to add in 4 more levels. I'm also glad you like the graphics — working with the Nokia restrictions was a challenge, but a pretty fun one. I'll definitely try out your game when I can!
I'm sorry to hear that the movement animations take too long. I could have them speed up significantly if you hold down the confirm or cancel buttons, at least on the enemy side, but adding a way to skip them altogether could be tricky.