Nice job! This game held my engagement for more than a few minutes, which is more than I can say for most of the other jam games. Here's a more detailed review:
Design [4/5]: I think the mechanics were explained to the player very well. The concept was easy to understand, there were varied enemy types, and I really like that every upgrade also came with a downside. The fact that you're constantly being killed by the parasite and that the only way to heal yourself of that ailment is by killing enemies means you have a lot of incentive to engage with the enemies rather than just running past everything. In general, the exploration feels fun. The graphics obviously aren't totally there, but I was still wondering what was lurking around every corner, which was nice.
I would have gladly given this a 5/5, but there was one thing that kept bothering me about the game design: I wasn't sure what the "potential" meter did from the explanation at the beginning, and I never figured it out from the gameplay, either. I also never figured out what triggered the upgrade menu to open. My theory is that the potential meter opened up the upgrade menu at certain intervals, but I'm not positive about that. I thought that could have been a little more clear, since they both seem to be essential parts of the core gameplay.
Adherence to the Theme [1/5]: I don't understand how this game relates to the theme. It's not obvious to me. It just seems like an FPS with a corruption twist.
Originality [5/5]: I'm honestly surprised I haven't seen another FPS out there that focuses on corruption. The corruption is basically a time limit you have to complete the level, and the green blobs you get from killing enemies basically just grant you more time (among other bonuses, apparently, but I'm still not sure what the "potential" meter does). That's a pretty simple concept, and I'm surprised I haven't seen any other games do that in either the indie or AAA gamedev scene. Then again, I don't play a lot of FPS's.
Overall, you've done a really nice job! Keep up the good work and keep working on games!