The graphics for the game are very nice and fit the aesthetic of the retro games it was obviously inspired by. The sound design is also quite nice. I... didn't like how floaty the controls are and there were times I'd fall off a moving platform if I was close to the edge of it.
The lack of a lives system didn't help, either, and the first area started off hard, introducing a lot of different concepts all at once. I'd suggest either removing fall damage completely (as it's inherently unfair) or allowing damage on things that would kill you (like spikes). Having both is a bit much since you're going to be falling a lot of the time and having spikes around to fall on is already enough of a punishment.
The idea of an autoload that Sugar & Spice suggested below would also be great. Having to go through game over and restart over and over again is beyond annoying.
Overall it looks nice and sounds nice but it doesn't play nice (as in, it will kick your ass). RIP Gramps. Forever.