There's a couple of issues I see, but this definitely has a lot of potential. Here's the stuff I think could be improved:
-The first thing the tutorial should mention is that you can rewind. This is a critical mechanic, and honestly, I almost gave up when I fell into the tutorial-pit and had a hard time getting out. If you know that you can rewind, though, it's a lot less frustrating. Honestly, I'd like to see features like this in more games.
-The rewind function is pretty buggy. It doesn't properly account for momentum or direction. This can be especially annoying when you mess up a jump and have to go back to the other side of the room to hit the wall so you can try again. However, the weirdness with the rewind does actually result in some fun scenarios sometimes- If you tried to use this intentionally and refined it, it could create some pretty cool mechanics, in this game or a sequel.
-There's not much indication of how powerful your jump is going to be. There seems to be around 3 frames of animation that play out at the start of the jump, but it keeps charging long after that. I'd suggesting either adding more frames as it charges more, or for a simple solution, simply "stretching out" the existing animation for the duration of the jump's charging period.
-The penguin looks really good, but most of the other graphics are pretty simple. That's not necessarily a bad thing, and doing a lot of graphics can be really time-consuming, but I would suggest at least adding a background, even if it's just a gradient or something. As it is, the levels feel kind of empty.
Aside from those things, I had quite a bit of fun with the game, the mechanics are simple but enjoyable, and as I mentioned, the rewind function means I didn't get frustrated when I had trouble getting past part of a level. Losing progress is one of my least favorite things in games, and this game completely avoids it. I'd love to play an updated version or a sequel. You mentioned that you might add more levels, and I'd be happy to play them, especially if you can improve some of the stuff I listed above.
Also, the twist at the end got me pretty good- It certainly fits the "Unexpected" theme!