What happens if you combine Super Mario Bros. with Tetris? This game is the result. Mostly you run around playing Mario until you can't advance any further, then you switch to Tetris mode to build structures that you climb.
I found it quite entertaining, with the end of the first level being particularly challenging! You control Mario with the arrow keys, switch between Tetris and Mario mode with the 'Spacebar' and rotate the pieces with 'X'. Enjoy!