As a game, it certainly wasn't particulary fun to play, that's how I felt as well.
I mean, did the actual gameplay have anything that made it stand out? Not just compared to the other Bioshock games, but compared to any other shooter?
Correct me where I'm wrong here, but this is how I remember it, from my only playthrough.
The levels were linear.
There were no alternative routes.
The corridor you moved in weren't particulary large.
There was no hub area.
There were no vehicles.
There were not standout physics.
There were no destructible enviroments.
There were no real standout weapons, as far as I remember.
It did the same mistake as so many other FPS where it hid ammo, energy and similiar stuff wherever possible, which made you run around and hit the button to pickup more then anything else.
The enemies were bullet sponges.
The enemies seemed to be able to hit you from wherever they were, and never miss.
It repeated the same encounters over and over again.
It repeated the worst boss fights.
The heavy hitters enemies were a disappointment.
So as a shooter, it was really really boring and unremarkable. The feeling after playing it was that I could just as well just have watched a playthrough on youtube, and not really have missed anything.