What a wonderful, charming puzzle game! I adore the art style and the concept is really well executed. With the music and sound effects, the mmod is immediatly set. I'd dare to say it is the perfect marriage ( :p )
As others have pointed out, sometimes it is a bit hard to know what you've collided with. But I think it would be a shame to put a grid over this art, so you could maybe change the size and/or color of the element we collided with to make it stand out?
I think the difficulty curve can also be a bit steeper as you progress through the levels. And I would also love a little animation when the characters meet!
Doing that game in 5 days is very impressive! That's typically the kind of game I wouldn't mind paying a few bucks for once it is finished.
(As a sidenote, this is the second time I play it. I didn't have any issues the first time, but today, the tab often freezes with both Chrome and Firefox. I don't know if there was an upate of the web build, but I saw that there is a downloable build. I'll check that out when I am home.)