As a big fan of the Wario Land series ever since I got the first and a GB Pocket in 1997, this is the series best, IMO.
Gameplay is your typical level-based platformer where you collect stuff. What's so great about the Wario Land series over other platformers is the awesome and useful moves, the big emphasis on puzzles that are actually fun, as well as the over all quirky feel. It's a lot like the last two Wario Lands in terms of atmosphere and transformations, just be warned that there is now a health meter unlike the previous two where you were invincible. I give gameplay a 9/10.
The graphics are just awesome. Not only is it good for GBA tech-wise (Yes, even to this day), it also just has an artistic flair of funk and weirdness. It's one of my favorite games to just sit and look at, so I give the graphics a 10/10.
The sound is a very appropriate fit to the games fit... That alone is worth something! I give the sound an 8/10.
Even though it was a little on the short side, I highly recommend buying this game.