The biggest noticeable difference in this version of Stronghold are the graphics, they are now up there with other big name RTS games.
The basic game play hasn't changed a great deal, still a game of getting the resources and building them into building and weapons.
The introduction of estates is a great little feature, taking some of the focus away from having to feed your people (estates generate food which is shipped to your kingdom).
The legendary units are quite cool. They can turn the tide of the battle quite nicely and are an invaluable unit.
All together a well put together game. A nice buy if your after a more in depth RTS.