It was a different team who made it and it just was nowhere near as good.
Partly true. Just before BioShock 1 was released by Irrational Games (which is the developer of BS1, and BS: Infinite) they split up into 2K: Boston and 2K: Australia. 2K Australia was involved in the development of BS2, 2K Boston wasn't. However, the 'core' team of BS1 remained in 2K Boston.
It wasn't a surprise to me that BS2 kinda sucked. It was hard to create a sequel especially if you consider how BS1 ended. Let's not forget the fact that you HAD to use that horrible abomination called GFWL. I've struggled hours with that piece of crap just to get BS2 working. It wouldn't let you save unless you downloaded a bunch of updates which had nothing to do with the game at all.
Also, if you played through BS1, and then immediately start playing BS2, the controls will feel wonky, especially since in BS1 you had to switch between weapons and plasmids, but in BS2 you could use them together. (You may think that'd be an improvement, but it still feels so awkward)
Now last year, before BS: Infinite was announced, 2K Boston changed their name back to Irrational Games. Having the core team of BS1 working on BS: Infinite made me excited for it. And from what I've seen so far it's definitely going to be a great game.