I actually found the gameplay pretty fun, even though it was simple. I love the look of the rooms with the eratic lamp placement! Level design is pretty good too, so good job on that! Im not the biggest fan of the story but that's just me, and I think you shouldn't spoil stuff on the end screen like you did. Strangely I tried to get into the secret room even before that ending screen told me about it but it just wouldn't work...
Maybe I would put a little more work into the art but it's 3d modelling and I can imagine that must take a while. As for the music, it's a shame the loop is so short, Id like to hear a longer version of it. Gives off a very mysterious mood...
Anyways, good job on a very playable fps with no annoying apparent bugs and non dizzyish controls haha!