They introduced a couple tweaks to the mechanics that were minor at best (the spear gun was an interesting addition, but I never used it since on easy it was simplest to go toe-to-toe, switching weapons only when forced by ammo shortages), but it's pretty much the same game. I didn't get the idea that 2 was "more" of a shooter than 1, but I suppose that wasn't really an aspect I'd be attuned to anyway.
So, I'd say the contrapositive holds—if you didn't like Bioshock1, you probably won't like Bioshock2 either.
Simply put, if the game's atmosphere doesn't pull you in, there's not much reason to play it. I got the game dirt-cheap on Steam, so while my experience wasn't great, I still got my money's worth.