Very interesting concept! I really enjoyed the physics of the key, that's a really good idea! The graphics are nice, and I appreciate the work done on the audio: the music is fitting and the little impact sounds for the key is a really nice touch (just a little bit too high-pitched for my liking ^^'). The different mechanics are great, and catching the key mid-air feels awesome!
However, all these awesome ideas are dragged down by the main problem of this game: the character has infinite acceleration and way, way too high terminal velocity, making it a PAIN to control, especially when the level design asks you to be precise. Honestly, grabbing the key felt like an upgrade.
Put the "key-grab" speed as the base speed, adjust the level design accordingly and you have a real banger. The potential is there, this game just needs a little bit of fine-tuning ^^.