Not the worst Tetris variant I've seen.
...but not the best, either.
Graphics: 6/10. Reasonable graphics and animation. Nothing stellar (except perhaps for the background, har har, get it, there are stars), but I know what everything is and the 3D effect is alright.
I dearly wish that you had included an option to toggle quality, however. There's a brief chance to right-click and toggle it during the preloader, but once the game starts, you're stuck with it.
Sound: 0/10. No sound? Really?
Playability: 8/10. Controls are fluid enough and the rules are sensible, and that's all that's really required for a game this relatively simple. Pausing when one clicks outside the flash window is a nifty thing.
Overall presentation: 3/10. The gameplay itself is solid and the graphics are alright, but the lack of sound, in-game quality control functions, and absurdly long into more than cancel out its strong points.
Ways to improve: Firstly, SOUND. Sound effects and background music are both necessary for a quality flash. Secondly, as I said, the ability to control quality level is a must---either don't disable it in the right-click menu or have a button, in-game or on the keyboard, that toggles it. Lastly, the intro is very long (another reason why quality control is important---it might speed it up a bit)---the whole 'light up the title' sequence takes so long that waiting through it for the game is...well...not worth the wait. Tidy up these flaws and you'll have a MUCH more solid game.