Game is quite fun! I think the demo ends after beating the 1st major boss, the Phantom thing?
I couldn't figure out anything to do with the candle. But overall, the game is great.
As for mistakes, I would look at your map rooms again. Once it gives you the map, you kind of get stuck in the pipes in both places (Brinstar and Upper Norfair). Eventually, the game frees you and lets you move again.
Also, I would make sure to alert people that you press start to save and maybe point out what it looks like. I've played Metroid games so I kind of knew what I would have to do to save, it actually took me a bit to figure it out.
Lastly, I would consider giving the player 8 directional movement. It would ease up on some of those jumps you have to make. It might just be me, but I find jumping harder when it isn't a B Button item. That being said, for a Metroid game it absolutely should not be a B button item, so good job.