This is a really cool and unique concept for an fps; I like it! Although I might've preferred if enemies had fewer numbers in their sequence in exchange for you having to do the numbers in order; I did notice that I was mostly just spraying with one number until the last instance of that number was finished, then spraying the other number until they died. It was still pretty fun as is though!
As for critiques, I got stuck on the "virus speaks the truth" puzzle my first time through because the password I got was "0000". This was the default state of the switches, but the door wasn't immediately open; as a result, I thought that 0000 wasn't actually the password and was searching everywhere for something else. It only worked after I changed the switches to a different combination and then re-entered 0000. It worked fine on a second playthrough when I got a different password, so I assume this was just an unexpected case. The time I spent on this puzzle also led me to run into the lag issue another person mentioned, since so many robots were spawning in the area I couldn't reach.
All the same, I think this is a concept that could expand into a full game really well; nice job!