Most surprising discovery/secret/unlock/experience in this game?

[starschwar]

Blowing up the Hind replaces them with hovering platforms when you go to the cliffs - Freedom Fighters influenced?

Here's one I only noticed as recently as Master Collection:  LBJ's voice changes.  Although only one actor is credited, he sounds much more haggard in the finale than he did in the initial phone call with Kruschev.  Perhaps a deliberate means of illustrating how crises like The Boss's defection can take a toll on political leaders?

The hovering platforms are based on prototypes from the 1960s.

I meant the gameplay mechanic.  In Freedom Fighters, accomplishing secondary objectives on one map would affect the other maps of any given chapter.  Blow up a helipad - no helicopters in the other areas.