PC Gamer has published a quick review of King's Bounty: Crossworlds, in which they hand the Armored Princess expansion pack an overall score of 78/100. Their conclusion:
The bulk of the expansion is less interesting. Orcs on the March is Armoured Princess again, but with some sloppy dialogue tree cock-ups, slightly more complicated Orc combat, and some more challenge-dungeons around the world. Loads of expensive magical items (which you can't afford) lie around in shops from the off, and there's a new Orc-centric quest chain, but it's still the same old world from last time.
Although Crossworlds won't rekindle your romance with the original Armoured Princess campaign, it offers enough content for veterans to justify the £15 purchase.