It's really cool! I like it! But here some bugs a tips:
It would be better if all the levels where in the same .exe
There is a bug on level 2, i get stuck when i try to collect the two keys. Also in level 3 there is a bug, once i get into the heart i can't get further.
At lvl 5 there is a bug too, i reached to the end, kill all the virus and there is no sign that says I won. The same at lvl 6. At lvl 7 there is a bug too. In one place it looks white and if you approach it you fall off the map to nothing and the game closes. Lvl 8 there is some bugs too.
Maybe something you could do to improve the game is that in some places there be something to reload the weapons. Because it happens that sometimes I shoot the virus that is asleep and sometimes it kills it in 3 shots and sometimes I have to shoot it several times to kill it.
ps: Hope you continue working with this project! The idea and graphics are great.