Some of my observations. (Note: I am not a profesional (or even good) game developer myself)
1. Auto-cannons audio gets a bit boring and stale after a while (especial with the 4 cannon gigantic titan)
2. Overcharge should scale too. It is super usefull early with the basic titan but next to pointless with the 4 cannon one. I thought its going to get more range or something as you tier up.
3. I love the controlls. Either shoot or move. (works really well with your ranged enemies)
4. The small basic enemies are hard to hit. (small hitbox?) So I got to lvl 50 and with my 4 cannon titan. Killing those bit red enemies was easy (literaly 3-4 shots and dead) while killing those small bastards was quite annoying.
5. I would like to see mouse position affect your cannon rotation. More focused fire if you understand. Would make it much more rewarding.
Anyway. Nice game.