This is actually a great version of the game, despite the genius of it ( turning the screen around ) , it's genuinely well coded and easily the best flash based version of the game out there.
I mean the gameplay and responsiveness of the controls plus the original Gameboy style of music, it's on par with well...... the original Gameboy Tetris ( which is for me the best there ever was )!
Besides, the fake TV scanlines effect is the best I've ever seen in any emulator, and I wish there was a way to use it in MAME or ZSnes !
Thanks for the link, it's a good find !