Thanks for your feedback.
First off, I never noticed if anything happens when the Psi-gauge goes down too much because for me it drained down to near zero and stopped, with nothing happening as a result. Secondly, a few checkpoints would be nice; I made a few reckless mistakes in playing where I got killed and had to start from the beginning. I didn't take that long to get that far in the game, but still it was annoying to have to restart from the beginning.
Yes the mana does not regenerate. Checkpoints yes ...
Edit:Finally finished. I noticed you can bring the psi-gauge down to zero, and I think the player can become stuck if they can't find a psi-energy pickup or have used them all already. Also the buttons to switch manually on the bottom only seem to get in my way because I used the number keys to switch weapons; I often stopped moving when I was trying to do something and the cursor went over a button. The saw enemies could also use a bit of animation in the saws, they look wrong not spinning. using the mouse to move and aim, I think limits the tactical options. If that's on purpose, then that's fine, but otherwise you may consider to split into mouse and keyboard movement.
Finally, I'd like to ask you what did you use to make the music? it was very atmospheric. And the term "megastructure" made me think of Blame!. If you haven't already you may consider reading it. It's not a normal manga, so if you hate moe and other qualities of japanese pop culture then you won't feel alienated reading this.
It seems not to be clear that the first spell : psi-fist costs 0 mana so the player can not be stuck.
The music is from
http://modarchive.org/.
Yes the game is inspired by Blame!.
Very nice comic.