Enter to start, arrows or W A S D to move, shift or up to rotate, and Z to undo the move you just regretted. Level, score and lines across the top, next piece to the side. Gamepads work in some browsers, and M turns the music off if the music is not helping.
The undo is the interesting choice. It removes the single most punishing thing about the genre, which sounds like it should remove the tension too, and instead moves the tension somewhere else: you stop playing safe and start attempting the stack you would never have risked. There is a settings screen for the rest of it, including how fast things fall, so the game can be tuned to whichever kind of session you are having.