Using Wario is refreshing, and there are plenty of funny references to other games, found in graphics but also in music, which are all very well done =]
The difficulty is OK but it becomes tough to the end.
After completing all the exits, my title screen shows 24 instead of the 23 mentioned in the game description above. Moreover, there is a little problem with level 3-2 normal exit, as it triggers nothing when beaten and thus seems not to count as an exit. In conclusion, it may have 25 exits in total.