What a great game, I love that oldschool PS1 vibe. The telescope effect was really cool too.
And having alternate endings and providing the player with choice is always a great idea.
And that is awesome that you got to work on this with your brother too, congrats on making a game together! (btw, 3D stuff is art too)
The main piece of feedback I'd have is the cursor needs to be locked for FPS games.