I have played some of the best 2D platformer games from Nintendo and Wario Land 4 is DEFINITELY one of them. Back in December 2011, I got the chance to download Wario Land 4 for the GBA and MY GOD IS IT AN AWESOME GAME!!!!! The humor, the platforming, the music, the gameplay and the exploration of the worlds is just what the game is offering to you in one GBA cartridge.
This is one of the greatest GBA games not to mention one of the best 2D platformers to date.