It's definitely a good game. Play control, atmosphere, and depth are all there. I also appreciate the 8 bit feel. It's like you're in the world of the original Metroid.
A lot of people are saying that the way the game goes buggy toward the end is intentional. Is it? While I was getting the last few gems, the sprites that make up the floor kept switching and the scene looked kind of junky. OK, in the original Metroid, a little part of the floor or wall would be the wrong color just once in a while, and when you moved away and came back it usually was back to normal. In this game, by the time I was heading back to the ship, the sprites were blinking and changing so rapidly, it wasn't always obvious what was ground or air. I couldn't recognize the places because they looked so mixed up. On top of that, I was getting huge slowdown and less responsive controls. If all those problems were intentional, I consider it a wrong and annoying decision.
If it wasn't for the bugginess at the end, I would have given it 10 an and 5. 8 and 4 aren't so bad though, are they? Thanks for making the game.