I have finished almost all the game in Game Boy including Mario.
finished marioland approximately 15 years ago
finished marioland 2 approx 2 yrs after that, literally the second time i played it (that one was so easy i never saw the game over screen even once)
even a slowpoke can finish those games. They r just too easy. fun, but easy.
If you want a *real* challenge, and you feel you are good at mario games I challenge you to play the latest true mario game, new super mario bros on nintendo DS.
It will bring back great memories from your childhood, while remaining tough and challenging enough to really give you a test of your skills and abilities! honestly that game is no 'toy' (like them marioworld and mario64)
(disclaimer: before the mario freaks here tear me apart, I know that marioworld and mario64 can be very challenging if you go to the special stages, etc. but the fact is you can finish them with absolutely no effort whatsoever. sorry guys, those games are for very young children. The last mario that was aimed at older gamers was Mario3, and thats what new smb is based on)