Wario is like the basic moments of different games mixed up and then thrown at you in a rollercoaster ride.
You get 5 seconds in which you have to figure out what to do and then do it. after a string of these minigames ( 10 to start with and then 25 at the end) you reach a longer boss battle which can be fiendishly hard. you only get 4 lives to complete the string of games in. the minigames hone your reflexes in preparation for the boss battles.
The actual games in themselves are very simple. you only have to use the d-pad and the a button. Its as if they boiled down games and extracted the essence of the gameplay. You start to realise that all games are based on these little moments. For example hitting targets, avoiding things and steering objects. they manage to put a bizarre twist on these basic themes in order to keep them interesting e.g. landing wario on a banana boat, aiming a finger up a noise and controlling a paper aeroplane.
The game in itself is very short but there is replay value because of a high score system and 2 player modes. The 2 player mode only requires one gba because you use the shoulder buttons. The game is very addictive and the learning curve is just right. This is a great game but it is on the short side.