In terms of controls and physics it's the best in the series. I feel fast and strong and in control as Wario more so than the other games. The sound effects for charging and hitting enemies goes a long way in this regard too. The short length makes it very replayable. I never played on an actual virtual boy but I think that's very appropriate for the system. Even if it's too short the difficulty curve around it's length is just right.
If I have to say anything bad about the game is that it's bosses remind of of Wario Land 1's in that only the final boss puts up a real fight. Sure the first boss's head weapon can get you if you never played the game before. (I guess so can that ghost dog in WL1). But it's just two fights where you watch them come on from the back ground and stomp the head after a heavily telegraphed appearance. Good use of the games gimmick yes but these are Mario bosses at heart