Not very much, and what it did it didn't do well, but it definitely had more than its sequel. Originally there were characters with dialogue and personalities--very stale and the voice acting wasn't very good, but at least they tried. The original had soldiers conversing with each other while riding in vehicles, the characters getting involved in the plot, scenes of the completely ridiculous villain--"General Guba" I think his name was. I'm not saying they were good, but they were there, and from a sequel I would expect them to have gotten better rather than nixed entirely, especially since they had already gotten incrementally better in the Resistance expansion.
I don't consider vehicles the "end all be all" but since they were an extremely major part of the original--that there were about three times as many missions, many of which put you in control of a tank commander or a helicopter pilot, there's plenty of reason to be extremely disappointed that they're suddenly absent, especially considering that there's no reason for them to be. The vehicle mechanics are there, and you can't tell me the plot didn't allow for helicopter or tank battles, so all I can figure is that we don't have tanks or helicopters because they didn't take the time to program missions around them.
The grandest thing about OFP was that it let you be not only an infantryman, but also a tank commander, a pilot, and, just for fun, occasionally a superhero who could be all three making for some very dynamic and enjoyable missions. There seemed to be no end to the new ways to explore the battlefield. That's what made it such a classic for me.
Not having these things doesn't make the game bad--it's not bad, but not great either. Not having them does, however, make it inferior to its predecessor.
That I paid fifty dollars for the game expecting at least the same level of fun and interest that I got from the original, and didn't get nearly as much, is impossible to argue, and plenty of reason for me to be disappointed.