For demo v1.02:
I beat the demo on Hard and didn't have any balance concerns. I spent a pretty good amount of time looking for all the secrets, but didn't find them. I think I ended up sequence breaking stage 2 by jumping from a tree up onto the highway; I'm glad the game lets you do stuff like that. Great music and visual direction, and the controls are fluid. Source-style crouch jumps are a nice addition. The further in I got, the more I was impressed. The attention to detail in the city really stuck out, but I shudder to think about what 10% of the Milky Nut is recycled.
You might want to lower the default sound effect volume some. I appreciated being able to break the cacti (PLEASE add a Steam achievement with the full release for breaking them all). The flinch effect on hitting basic enemies feels really good. I did find that the saw-hand enemies had a hard time navigating stairs. The secret jingle is great, but also way louder than the rest of the music.
The controls menu is a little wonky and could use a little work if you get to the time. The setting for which controller you're using being the only text heading in the menu made me think at first that all the settings below it were for XInput Controller No. 1, so you might want to encapsulate the text in a box together with the Select Gamepad UI elements. Gamepad selecting being a scroll bar instead of radio buttons is also bizarre, but if it works, it works. You might also want to add the text about pressing a bound key to unbind it in the popup text where it says "Push a key/button to bind to [INPUTNAME]." These are minimal concerns, though.
I didn't know that alt-fire actually did anything until seeing the "walk while zoomed in" option while writing the above. It might be a good idea to throw up a tutorial for alt-fire somewhere, like maybe when you pick up the first SMG, then another saying "some weapons have a different alt-fire" when you first grab the shotgun.
I did find one tiny bug where walking off of some surfaces would instantly kill your horizontal momentum and you'll fall straight down instead of running off; it happens sort of consistently but not every time with the little standing lights on level 1 (pic related). It also happens sometimes when running off the roofs of cars.
I also try to make a commitment to getting into places where I'm not supposed to be, and in the start of stage 3 where the magenta terminal is (near the mech enemy), I jumped from the boxes to the slanted pipe onto the building, and you can see OoB. If you walk into that garage area on the right, you get softlocked.
I had a great time with Ctesiphon and I'm excited for more. You did a damn good job.