Solid platformer - nothing really special - kind of relaxing to play through (the music helps here). Just collect the coins, avoid the spikes & explore.
Didn't mind the slippery movement. Double jump can be annoying when you hit an edge/wall during a jump - it means you don't achieve the max jump height - which is important for some platforms - not a bad thing - just an observation: shouldn't be a problem for good players... although I'd make the double jump a few pixels more - a little more forgiving on players ;)
Recommend adding a story: platformers is a crowded genre - so a good story is the best way of giving a game a bit more depth (I didn't say it's the easiest!!)
Also need to think about do you want it to be a collect-stuff-for-no-real-reason game, or maybe an actual adventure platformer. Simple changes: Instead of coins - power orbs (they could be the bloom of a flower common in these parts...). Need power orbs to power next gate. The ability to shoot is then a special type of power orb... which introduces the ideal of equipable power orbs (destroy weak-rock, freeze, fire, solidify mist, bloom flowers...) thus giving you the opportunity for more terrain types to interact with - and if you can only carry one equipable orb at a time, the opportunity for some interesting puzzles... (OK, so maybe not so simple changes ;)
Anyway - lots of potential here - a solid base to work upon - I didn't find any bugs, and everything worked as expected.