I really enjoyed your game! It ended up being quite easy, but I can understand that balancing that might be really hard. I preferred the double colts, the other guns weren't as good and it was harder when I didn't have them. Once I died, it was harder to get back up with the energy cells.
Restarting from the same level is probably good for most players, since then you don't have to grind the easier ones again, but if you add a hard mode just push the player back to the bottom and start as a "new" robot, it would be even cool if your old body would be found on the level you died, this way while you climb back up to the roof, you would see all the unfortunate bastards who didn't make it :D