My cronies and I have played KoenigsKrieg for 30 years. We like the new edition very well.
The rules have been cleaned up, reorganized, and many ambiguities cleared up with explicit rulings and examples. There's even a detailed flow-chart of exactly how to play every phase, sub-phase and pulse of a complete turn. Naturally, the rules are a bit longer than they used to be.
Little has been intentionally changed, but the rules play some differently than they used to, because the general trend is to close loopholes and limit gamesmanship in favor of more historical play. There *are* some new troop types and special rules, especially with regard to non-European armies, which I think are better represented than in previous editions.
I like the way troop point values and army organizations have been revised. These changes encourage play with balanced, point-limited forces. 1000 points per side gives an excellent small game. More experienced players with more stamina can play with bigger armies. There is also a set of small historical scenarios available for when you get tired of balanced meeting engagements.
I still don't recommend KoenigsKrieg for big historical battles of the era. Too many troops and/or commanders overload the rules. In My Opinion.
Executive summary: A solid upgrade to a classic set of rules. Buy it.