I liked it very much, gave up at the last level but I'll try more later.
It feels just like a GB game, and by that I mean that its a bit clunky. Most of the time it's not the platforming that is hard but being able to jump from the grappling hook. Sometimes I have to press more than once so that I could jump. It would be nice if you added a button buffer so even if you press the jump button before you're able to jump again you have a little leeway. Besides that it was a very nice experience.
I'd recommend toning down a bit on the inertia, as I think it does not match with the style you're going for. If you're open to suggestions, you should add some puzzle mechanics with the grapple too, I think it would be interesting.