Ok, tetris DX is playable on any gameboy, it's on a black cart.
It adds a score system (and a power level), improved 2 player, but crucially, it fixes a minor niggle in the original that the blocks are less sticky when they land. If you're serious about tetris, you realise how important this is. The original wasn't broken, but this little tweek brings DX up to perfection.
The original was a 9.5 out of 10 game, and DX is 10/10. I just wish it had the music from the original.