There are 24 levels in total so far, I haven't finished it myself yet, but as far as I've read/seen you can either complete the adventure you've started (all the coins etc.) or you can start again but this time with stronger enemies.

It is also possible to play individual challenges or training units without a "story", so that, for example, certain muscle groups can be focused on. In this way, you can put together your own training without having to "experience" the same story again and again.

You get additional countries. But they are not as extensive as the normal ones.