Take any game and compare its released version to a build from three years ago (if it even existed) and you're going to notice more than a few changes. BioShock Infinite is no exception and while we can't dig through Irrational's source control for a previous iteration of the game, we can use old videos as a point of comparison.
Note: Even though the video above is from 2010, it could be considered a spoiler.
I have yet to play Infinite, so I can't make any comparisons myself, but this Reddit thread, which invited readers to play spot the difference between the retail version and a gameplay video from 2010, points out that Elizabeth no longer has telekinetic powers or the ability to control the weather. It also appears a few mechanics were modified (such as Vigor usage).
While I'm sure the changes were made in the interests of delivering a better game (and getting it done on time), is there anything missing that you wish Irrational had kept in?