A nice game! Agree that the plot could be a little more involved, or maybe you could just add more detail to the environment and more stuff the player can interact with (like someone left a book, a few banana peels here and there, idk).
You could probably make the movement a little smoother. As far as I can tell, right now the player just moves in a specific direction when a key is pressed. You could instead make the player accelerate a little toward the maximum speed, and/or make the camera wiggle sideways, imitating human movement (but not too much, otherwise the game would feel too console-ish, - but that’s just my taste).
I noticed you can double-jump in the game: not sure if it’s a bug, but it doesn’t seem to be particularly useful.
You could also add a simple distance fog - right now the far clipping plane is noticeable if you look from the first/last car into the tunnel.
The lamps seem to be point lights? I don’t know much about Unity but I’d guess that it should have support for area lights to make the scene look more realistic.
By the way, I tried the usual Linux version an it didn’t work for me, exiting without any errors reported. The GL Linux version worked, although with noticeable artifacts - a lot of what seems to be z-fighting (in both the scene and the shadow maps) and floating-point issues. Looks like you do already know about this issues, but I’ll add a few screenshots anyway, in case it helps.
