This is a great idea, I'd love to see a full version of it, but here are a few ideas:
- As Heliopause545 stated, a turn based option would be an interesting idea. Expanding upon this: perhaps make it "puzzle based". I.e. you are given 4~ blocks to work with and once you reach the end of that you are given more blocks to form your dungeon after fighting a miniboss of some sort. Then the goal is obviously to level up your character as high as you can before you reach the top and have to fight the "'final' boss", which if you win you go to the next "level" where pieces fall quicker during the building segments(and you get more pieces at a time) and the final boss gets tougher. But if you lose your score is recorded and perhaps there is some sort of rogue-lite element where you unlock more items/pieces or what-have-you.
- Either try to get Tetris on board(no idea how you'd do that... plus you may get screwed out of any money you may make if you do get Tetris branding, or you could possibly make a butt-ton of money, it seems like things could swing either way. There is just a lot to consider for this) or move away from the Tetris theme so you can legally sell this. DO NOT MOVE FORWARD ON THE TETRIS THEME WITHOUT EXPLICIT PERMISSION! That would just be begging for a good ol' fashioned C&D. Try different shapes(perhaps random blocks of 6? IDK), maybe move away from the "line clears"(maybe the only way to change the board is with your character instead of how blocks are placed), and definitely change the grid size. I don't want to see this idea go to waste, because it is a damn good idea.