I beat this over the holiday weekend and got 100% map and items (except for that secret gun that's random for each save file and doesn't count toward 100%). Awesome experience overall and definitely the best Metroid clone I've ever played.

With a game with 20 or so guns in it I would have expected most of them to be useless. And for the most part they are. However, I was pleasantly surprised that a good 6 or 7 of them were my main gun for quite a while and various ones had different uses depending on the situation.

Like Unne said, the upgrades to movement to get to new areas were very innovative. No space jump or jetpack in this game! Getting to some of the trickier areas was very tricky since you had to combine a few abilities in ways you wouldn't normally think they were for, but I enjoyed that challenge.

I will say that the bosses were really easy but maybe that's because I would backtrack every time I got a new power up to unlock all the areas I missed.

Really fun game and I am impressed it was developed by just one guy. I hope he makes more.