I freaking love Tetris so much, and I've been going through rating (browser-playable because I'm on a Chromebook, and downloads are possible but difficult) games by least-rated, and I've just been dying to get to this already. I knew I would love it and I do. It's hard for me to feel any other way about it because of my love for Tetris.
My weird Tetris obsession aside, this really is just a cool concept that's been executed really well. Some letters are just terrible, but it adds a sort of wacky charm. I agree with another comment that a bigger board would probably be nice, and suit the letters better.
I hope you have plans to keep working on this. With only a little more work it could be a completed game, and I want it as a completed game. This also gave me the idea of a multiplayer mode where words you type are the other player's blocks...? I don't know. You probably don't need my goofy ideas; it's just that I love this and I love Tetris, haha. Awesome work!