IonDistorter
I just saw your review. The game is NOT a multiplayer live-service game it's a singleplayer only game, not even co-op. The boss war / death match will be with AI like you can spawn bots in cs 1.6 and play. I don't know what is your computer, but I've tested it on my 13 year old laptop with a very old GPU and the game runs with 30-40 FPS, on GTX 1060 (nearly a decade old gpu), it runs with 60-75 FPS. I have a player on Mac who is running windows as a VM and gets 50-60 FPS and on my RTX 2060 the game runs with 200 FPS. It's either your GPU, drivers or something else that I don't think I can optimize since you mentioned it runs bad even in the menu that only has a single character and a UI, maybe press '/' and check your console logs, if it spams errors then it might be because of it.
The music - calm transition to combat is like I mentioned the style of Doom.
Character creator and NPC thinking you are different and why the character's name cant be changed: It's a biopunk game, in such a world you can customize yourself and also I wanted to make a hero shooter, so there's no option to change the name. It's like changing the name of Geralt from the Witcher.
I'd be curious to see how you can slap a few assets together in unity and create this in an hour though.