Battles of Ardania comes with an 8-mission campaign where you face off against a powerful werewolf. The werewolf doesn't attack you directly, but instead influences others to turn against you and your allies. That means you have to defend Richard the Lion's Share and his Traders Guild from attacks, foil an assassination attempt, and cleanse the realm of rat paladins (and the ridiculously powerful rat seneschals) before eventually focusing on the werewolf himself.
Monster Kingdom comes with a 10-mission campaign. In it, you're deposed as king, and so you have to use your former enemies -- the monsters -- as your allies to take back what is rightfully yours. This is a fun change of pace for the game, as monsters take on the roles previously filled by humans (goblins archers act as rangers, liches act as mages, minotaurs act as dwarves, and so forth), and you use them to defeat human kingdoms.
Unfortunately, possibly because Monster Kingdom came last, it's the sloppiest entry in the collection. The written text is full of typos, the spoken dialogue never matches the written text, tax collectors never pick up gold from goblin mines (which take the place of human windmills), and the last mission crashes like crazy (probably because there's a huge number of enemy units). Monsters also seem to dislike exploration flags, and so it's tough to get them to reveal the map.
Along with the 42 campaign missions, there are also 16 solo missions. Most of these missions are of "advanced" or "expert" difficulty and take 2-3 hours to complete (at least if you're like me and play them at half speed so you can react to everything). That means the Majesty 2 Collection has over 100 hours of content, easy, which is a pretty good deal for its $20 price tag.
I didn't find the missions to be too overly tough. Majesty 2 has sort of an unfortunate quality where all of the missions play about the same (with only the harassing enemies and final enemy being different), and so once you've found some tricks and strategies that work (like always building your marketplace first), it's usually just a matter of grinding your way through the maps.
Majesty 2 does have some annoying bugs that were never fixed. Most notoriously, loading your game can cause scripts to fire early, and so you might have werewolves attacking your kingdom on Day 4, or a dozen minotaurs and a dragon attacking on Day 19. Events like these guarantee that you're going to lose the mission, and they're annoying when they happen after you've invested a lot of time building up your heroes and kingdom. But on the good side, Ino-Co brought back George Ledoux to play the advisor for all of the campaign missions, and his acting ability alone goes a long way in making the missions more enjoyable to play.
Overall, I didn't like Majesty 2 as much as the original Majesty, given that it watered down a lot of the features that made the original game unique, but Majesty 2 is a solid enough real-time strategy / RPG hybrid, and with all of the content bundled together in the Majesty 2 Collection, it's a pretty good deal to boot. So I don't have any problem recommending the collection, and if you're feeling expansive, then you might want to spend an extra $10 to get Majesty Gold as well and see how the franchise started out.