Dr. Mario is often bundled with its more famous predecessor Tetris. The puzzle game is certainly a worthy successor. While there are versions of this game on more recent consoles, the straightforwardness of the Game Boy is something the more recent ports lack. The game is fast, the music fantastic. Simple and a lot of addictive fun.
Have a look at “How to play retrogames?” if you don’t know how to play retrogames.