The game's out in Japan now:
Since it's free, you can just make a JP account and get it if you want. Basically, it's identical to Puzzle & Dragons and the recent Dragon's Dogma Quest, except you play Tetris. The menus are scarily similar, and nothing about it -- aside from the actual Tetris part -- feels like Tetris.
The thing is, I think it might be better than Tetris Blitz. I know that game gets a lot of flack, but I think it's basically the Tetris the world of touchscreen gaming needs. But while that game has absolutely no depth, Tetris Monsters has at least some RPG elements to it. Plus, it hasn't bothered me to connect any social networks yet, hasn't tried to get me to buy anything yet, and seems to load/play faster.