I see what you mean. Perhaps it shouldn't look like piss but I'm happy to hear it looks like liquid.
Making people melt sounds like a good idea. Would be hell to pixel though.
The green stuff is supposed to be organic like grass or some space fungus thing. The ground tiles are irregular bricks/rocks and everything between is just dirt, mud and stones.
I wanted to get a feeling of something not exactly human but still humanoid.
Here's the latest update, did work mostly on the HUD.
The ammo section should only show the ammo for the current weapon.
It now displays ammo for the stun-gun, dart-gun, acid-jet, rocket-launcher and the grenade-chucker.

I feel that it's not as other-worldly as I had hoped for though, currently it almost looks medieval which wasn't what I was going for.