Very unique sound out of the gate - Opening explores a couple of different moods I think. The choice of synth patches at the beginning was interesting and rather textural at points. The change of pace and introduction of percussion for the final stretch was a nice touch.
Stage Select sounds rather ominous! Descending melodies always tend to have this effect, but the choice of voicings helps sell this, also. Seems like it is set up to loop without issue so that's a plus!
The Pause Screen melody is kind of haunting in its own right - pensive and awaiting continuation. I can't remember a ton of games having pause music specifically but this is a neat idea and it is executed well.
Final Boss has a great set-up - the choir from the get go does a great job of setting the stage for what's to come. Nice choice of melodies and waves for carrying the main theme itself, and I'm going to take this opportunity to say kudos on the percussion - nice and frantic but keeping the core rhythm going to bolster the rest of the track. I think this track is my favorite of the set, personally.
All in all, good work! Some neat chiptunes here, I can see them being put to use in a variety of games. Nicely done!