I definitely get the complexity can grow a lot. Even regular Tetris has some fairly mind-blowing mechanics that a lot of people don't know about and it's best to keep things simple and fun.
If you're looking for inspiration and aren't already aware. TETR.IO (https://tetr.io/) is basically the gold standard of Tetris games on the PC. You could probably get a lot of ideas on look/feel by playing around with that.
Best of luck!