A real pretty game and one i will be looking forward to.
The environment and general atmosphere hits the spot just right, so even with the homage to Metroid missing, fans will clearly be able to tell how much the game was inspired by it, without being a literal copy.
The Oxygen is an interesting feature though i'm not sold on it yet. It decourages exploration since the urgency of not running out of air is high, since players are unable to tell when they can take a breather again or find a new save point to reload on it. It really depends on how you'll add to this feature to get me better hooked on it.
My only Issue would be those Crumble Blocks unlocking secret areas, or just normal progressions, they can be hard to see and if there was a "learning" section about them, it clearly didn't last for me.
Using them for Secret Areas only would be much more rewarding, since they can be hard to find, while using them for general progression just makes them a tedious staging element since you'll need the one correct spot to shoot at to progress.
Looking forward to this Game. :3