Thank you for your feedback!!
1) Yeah, instead of doing that I decided to set up multiple checkpoints in some levels, so that the player doesn't have to wait a lot and redo all the level after a small mistake. Will try to update and make it faster later.
2) In the intro I made Astro go through one of those portals to start the game, hoping the player would associate them with progression. XD I didn't want to implement many tutorials, just the most important stuff the player needs to know, and let them experiment with that.
3) There's a problem with the WebGL version of the game, where you can't see the whole screen for some reason. The only solution for now is to play on fullscreen. I left a warning in the description. Sadly, I have no idea how to fix that, and I didn't have time to upload a PC version. :c
4) Yeah, my bad lol. I added them to the game, but messed up the level order.
Again, thanks for your feedback! Helps me lot. \o/