The next level objective is to retrieve the cat. The typical level is not overly large, taking from perhaps a couple of minutes to at most 15 minutes to complete. This means there are a lot of levels and you don't often retrace familiar steps either. I found this kept things fresh, and always meant I was wondering what might appear around the next corner. Very nice indeed.
Level design is generally of a high quality.
Things make reasonable sense on the whole when you think about the location the level is attempting to model. I found the difficulty level was reasonable. On easy the enemies are essentially passive, while on the harder levels you'll need to collect all the power ups you can to make it through in one piece. Only in a few cases was I frustrated with a level. You ended up having to ride on top of a tram through a tunnel when it is clear there is not enough room to do it.