Very entertainig. Fantastic graphics, sound and atmosphere. Heavily influenced by Super Metroid in the best way possible.
I heard some say it is very hard. They probably never played NES games. I disagree. I could defeat most bosses in just a couple of tries.
The alien environment is absolutely beautiful. and rich in every detail. Gorgeous. I love the strange sounds the creatures make. They feel organic, real... Sometimes cute and funny, sometimes even sick and disgusting, and they fully transmit the sensation of something alien and alive.
My only suggestion would be, please, add the names of the areas to the map, and a couple more fast travel robots in key places. That's it. Other than that the game is great as it currently is. Extremely recommended if you are into Metroid like games.
To the developers:
Thnak you, I loved your game.
I would also surely pay for some extra content to find out answers to some in game remaining questions (not all of them, cause having some mystery is also a good thing), and to know the back stories of some important characters.