I like the style and sounds of this game a lot!
The core combat is actually really punchy and satisfying to play. I particularly liked using the shotgun.
I'm not really sure this can be classed as a boss rush when it has hordes of zombies in-between bosses like that. It kind of just feels like a normal fps game, also the spin mechanic I just found to not really be useful 90% of the time until the third boss requires you to use it to stun them.
I couldn't beat the third boss either because by the time I'd spun around they shredded me with the black hole(?) attack that I couldn't even really see and I'd just die in a second.
I would've liked it more if it was just boss after boss and you could spin the gun instead of your whole character since it got very disorienting but maybe I'm just not that good at 360s.
Honestly if you just ditch the boss rush thing and maybe rework the spin mechanic this would probably be a pretty fun complete boomer shooter.