Finished the SP today. The difference from start to finish was quite big. From the Vietnam mission onwards, the game became more fustrating in places: more AI enemies just shooting at you, you personally doing everything, annoying restrictive scripting came more obvious.
This all annoys me, as the setting, and the story I both enjoyed (as much you can for a blockbuster dude-bro game), as they fitted each other well given the era. Further, the implementation of swimming, an unusual story telling method, the use of other vehicles were good/unexpected inclusions.
Spoliers below:
I'm warning you!
For the story itself I wasn't expecting the JFK assassination, as it seemed too likely, something along the lines of Reznov being a triple agent getting you to do somesuch with the NOVA 6 gas against America (with the backstory to him turning out to be lies, fitting in with what he said about being lied to by others) was my guess. But I'm kinda glad they did go with the JFK idea, quite a good conspiracy theory to stick in. One thing I did expect after that was another twist, with Reznov being actually alive, perhaps in Cuba smoking a cigar on the beach, leaving you wondering which (if any) of the missions he was or wasn't actually in.
Spoilers above!