I played it, and here is my review:
Pros:
Simple level design.
The toxic barrels looked cool
I love the angle at which you hold the gun.
Fun gameplay.
Cons:
I was able to jump out of the map
I was able to skip a level by pressing one of the function buttons (F9 I believe) although I don't think this is your fault, so leave this one out, but I suggest looking into it.
The text on the screen reappears everytime I step back in the trigger zone
At the beginning of level 2, when I look back, the cave I came from is blocked off. Maybe add some invisible walls. Likewise at the end of the same level, you can see outside of the map.
Overall - 3/5. A game with lots of potential, it just needs a little bit of tweaking.
Putting the fun back into Fungus since 1984.