I like Tetris and so i liked this too.
In the beginnign it is not quit clear that you switched the core mechanic from rows to columns, but in my opinion this needs no extra explanation because you get it after you have seen it a few times xD
I stumbled upon a bug which didn't let me finish the game:
-Columns get destroyed when 4 points are upon each other
-first item the long willy
-put it upwards on the ground
-it disappears
-no new blocks spawn
I hope it is precise enough so you can figure out where in your code the mistake is. Maybe the same softlock Tameno posted.