Its a medieval strategy-based game, and you can have different AI opponents. These characters talk to you at times (a video thing pops up, showing their face talking, and you can hear it), and you can talk back (or at least, your allies). You can select which AI characters are your allies, and which are your enemies, and you can setup various teams. Its pretty sweet...
I've played it countless times, with practically every combination possible, and I win everytime. But in case you think its easy...its not. The AI opponents are very clever, and they use different strategies and units to fight against you.
In addition to building a castle and army for defense, and attack purposes, the game is made more challenging and fun by forcing you to keep your people happy by providing them food, and other things. If your popularity value gets below 50%, people start leaving your castle, starting from the workers, until even the unemployed peasants begin to leave. You can get gold by taxing the people (which, btw, lowers the popularity), and/or by selling material goods (such as stone, wood, etc.) at the marketplace. Military units can only be trained if you have enough gold, and the resources each unit requires (for example, to build a maceman, you must have enough gold, at least 1 mace, and at least 1 leather suit of armor, which are created in weapons workshops). A mercenary post allows you to train Arabian units for only gold, but they are understandably more expensive. There are lots of different units, with different capabilities, such as the assassin, who can scale walls with a grappling hook, and who is invisible to the enemy, except at real close range).
The AI characters' names are as follows:
Rat (this is the easiest opponent in the game; he's not much of an enemy, as he uses only spearmen and archers. These units are easily killed)
Pig (this guy is a fat character who likes to use macemen, and crossbowmen; he's a fairly good fighter, and will attack sometimes with a very small force, and othertimes with a huge force. he also uses siege weapons such as a battering ram, and catapualts, but when you know how to beat him, he's not much of a match)
Snake (this character prefers the dirty methods over an outright attack; he'll always be sending slaves with torches - procured at a very small expense, namely 5 gold - to try to set your buildings on fire, but he'll attack often with spearmen, archers, laddermen, catapaults, and a few other types of units)
Wolf (this character is one of the toughest in the game; he knows how to rule his castle with an iron hand, and still retain enough military force to send against you, and any other enemies; he builds different castle defenses, sometimes surrounded with moats, and he uses square towers with siege weapons atop for defense, along with crossbowmen and archers; he usually attacks with swordsmen, pikemen, crossbowmen, and siege weapons)
Saladin (this character is based on a real-life Muslim commander back in medieval times, who fought against the Crusaders, and conquered Jerusalem from them; if you watched the movie "Kingdom of Heaven", then you know about him; in the game, he's a clever Arab lord who knows a lot about desert warfare; he runs his economy well, and will always be sending out arabian archers, horse archers, arabian swordsmen into the field, whilst at the same time building up a decent-sized force at home. Probably the best way to defeat him is to set his whole town on fire, and reduce his castle to a smoldering heap)
Lionheart (this character is based on the historical "King Richard the Lionheart" of England, who fought in the third crusade against Saladin; in this game, he's one of the tougher opponents, and perhaps the best at attacking, of all the AI characters. He uses catapaults on square towers for defense, and tends to keep most of his fighting force on the castle keep, while only sending out military units every now and then (between attacks to his enemies) to defend his economy - i.e. farms, and other work buildings - so they wont be destroyed by enemies. He uses mostly armored units, with the exception of archers, who wear no armor, and are fairly useless in hand-to-hand combat)
Sultan (this poet character is not much of an opponent, but he'll always be sending out slingers, arabian swordsmen, and arabian archers against his enemies)
In addition to Stronghold Crusader, they also have a Stronghold Crusader Extreme, which I've only played a demo of, but which allows hundreds of thousands of units in the game at one time (Stronghold Crusader only allows a few hundred). The real fun thing about the game is, it looks mostly real. The characters all talk, and you can give them commands (or at least, the military units). Military units can only be "trained" from peasants sitting around a fire in front of the castle keep, workers can be created as well which will work at all the various buildings (ranging from farms to mills, weapons workshops, and a whole lot of other buildings). Some of the workers can fight when they encounter enemies (for example, the woodcutter will fight any enemy units he comes close enough to with his ax, and the hunter will shoot his bow at enemies who come within range). Once assigned to a task, a worker never leaves it, and will continue working indefinitely throughout the entire game, unless he is killed or the building he's working at is destroyed (in which case, the worker becomes a regular peasant again, and goes back to the fire in front of the castle keep).
In short, this game is really cool, and whoever who reads this, should try it out sometime.