Almost fun. There's a few nagging problems that keep it from being. Since everybody loves lists, that's I'm doing it that way, counting down.
(5) For some reason, doesn't quite work right on my main browser. Ik, not everybody uses mine, but plenty do, and don't install others (i.e. Chrome [blargh]) for whatever reason, just like me. Game works fine in at least one. I didn't know this until a good ways in, and it's only the jump that's bugged. That means having to restart after you hit the platform section in the far east. It looks like you should make it, yeah, but you just can't. I don't know why. It must be just a pixel off or something. Weird. This is what happens, though, when you make a game pixel perfect. Don't do it.
(4) A little clue might be nice. Okay, so it SHOULDN'T be too hard to figure out that the dagger can cut the vines, but I only figured early on since the levers weren't taking care of them. "It might help you in other ways too." Good enough. We don't have to baby people.
(3) Just a little explanation. Even just a few words would be nice. Something like "This is a checkpoint. Use the action button to save." It helps wonders. Technically this probably covers as well.
(2) Better placement on checkpoints. They always seem too close, or too far away. Can't really elaborate more on this one. It's a level design issue. Actually, I almost think there are too many overall, but we're obviously trying to make a not-too-difficult game here. I get that.
(1) The music. I get this too. Just like the "monochromistic" colour scheme, we're going for minimal here, except that it's somewhere strange between VCS and 8-bit era. It wouldn't be bad, except the loop is horribly short, and the melody itself average at best, if even. That means that unless you're lucky enough to have a browser with a Mute Tab function--I didn't see the mute option explained until after the game, btw, you need to do this in game, perhaps at the title screen--you're stuck with whatever is playing unless you turn your system sound down or off completely, and that's unacceptable. I'm sure you can either put some small effort into making something--or requesting something of somebody else--that's bearable for the 10-15 minutes or so it takes to play the game. If not, try to stick to the era you're trying to represent.
That said, I have no problem with the graphics. I've seen a few comments berating that, I dunno why. Maybe it's because when I was a kid, I had an original GameBoy stuck in my hands, not a Nintendo DS, eating through four AA's a pop until the late 90's. Then again, maybe I just appreciate these things more, and that's why you're getting 2.5 stars, and not one or 1.5. It's an interesting game, but there needs to be a little more effort to make it something enjoyable.
 Blast. Sry for the text wall. Guess I went a bit overboard.