Awesome!
I'm actually a bit stunned - I don't think I've seen the exact mechanic before.
If you came up with a concept that simple, I think it's really an achievement. The swapping makes intuitive sense and you can immediately see this having a similar appeal to classics like tetris. Really hard to come up with new concepts in this space. Then again, I might just not know them - still very enjoyable game.
nice music and great art - the icons read very well and are clearly distinguishable.
My only gripe would've been the controls section. When I click on 'controls' I would've expected a short explanation of what the buttons do, similar to what you have in game. Swifting through a wordy pages about the lore etc really wasn't what I was looking for at that point. ^^°