Played until the level with 2 buttons that refuse to be pressed at the same time. (impossible?)
Update: Got past the level by deleting my save file and not picking up speed downgrades. Now stuck in the boss snail room, since killing it doesn't actually open the door and you'll be stuck.
Talking about the boss, it sucks. Another thing that sucks is getting hurt offscreen by big snails during a door opening cutscene. There is also a level where killing the snails in the wrong order makes you get stuck behind the open gate.
Other than that, pretty fun game! It uses the limitation well, and it's quite fun to play. Good job!