There is two Mount & Blade games. There's the first game that's named only Mount & Blade but you'll want to pick up Mount & Blade: Warbands because Warbands have all the features the original game had including new animations and new items. Also note that the video below is Warbands footage.
Mount & Blade was developed by the Turkish TaleWorlds and published by Paradox Interactive who are also known for publishing titles such as Magicka, Galactic Civilizations II and Lead and Gold: Gangs of the Wild West. Mount & Blade is primarily a medieval sandbox game / RPG.
You start the game as a foreigner in Calderia and when you arrive you get attacked by a single thug in the middle of the street. A lonely merchant hears the commotion and suggests that you take care of it. This is meant only as an tutorial and you can refuse him in order to set your sights on bigger fish. You might be thinking why I'm calling this game a sandbox for then? Well, firstly you can more or less fill any role you might desire. Do you want to be a peaceful trader and create an economic empire? Yes, you can do that. Do you want to be a raging warlord in the service of a king, you can do that too. You can even become King yourself and hand out fiefs to your vassals which will attempt to protect them for you and gather armies in your name. Or you could just run a mercenary company in order to keep your freedom.
Lords, ladies, kings and death
In Calderia you got strict classes in society. Firstly you have the Nobles of Calderia, they will mostly wage war with each other but will work together and against the player depending on whenever they trust the player or not. In the case of war the King will elect a Marshal that will lead the nobles during a war campaign. When they manage to capture cities and castles the Nobles will start to vouch for people who should be awarded these prizes. Since fiefs gives a weekly income to the lords they will not back down from receiving one if they can help it. The player can really try the game of politics and persuade the nobles to "vote" for him so that the king will decide to award the fiefs to the player. The player can get the respect from other lords by doing favors for them or participating in battle with them. The marshal will be especially grateful for the people that answers to the call of battle and will most likely be one of the key contacts the player will have.
And here is where Mount & Blade shines: It's the politics system! You will be challenged throughout the entire game because the Calderians are very stubborn and old fashioned. The game will try to gather the lord (which are often spread out over the land) by hosting feasts in various places. There you can "court" ladies of the realm and possibly get a bride one beautiful day. The lords will also be good associates that will gladly help the player in the player's pursuits. The NPCs are somewhat flexible in this regard but
The game does have it's faults though. The AI of the opponents are somewhat weak and the controls feels a bit clunky. The characters in this game are very stiff and it will very few times be worth the effort of jumping (unless you're on a horse) and you will often curse the sluggish movement speed the characters have. The animations for attacking are uncomfortable and it's somewhat hard to aim thrusts. The bots doesn't seem to have that problem though and will pretty easily pull off quick and well aimed thrusts and chops at the player.
The multiplayer in Mount & Blade: Warbands isn't perfect but it's very solid. You pick a gameplay mode: Conquest, Capture the Flag, Duels, Sieges, Deathmatches, you name it. And when you're in the game you pick a faction, a general class (Footman, Archer, Cavalry) and then you customize your gear. You don't have access to the entire arsenal of weapons but you have to earn it by killing opponents. The system rewards skilled players by making them harder to beat next time they spawn. Multiplayer in Mount & Blade is really difficult though and expect to fork out just as much time as learning how to play Team Fortress 2 at least. Some servers disables automatic parrying and enables friendly fire which beginners really suffers from but on the other hand, it does counter spamming 2 handed swings and blocking monsters pretty well. It will also make fights look more like a medieval fight would look like and could encourage teamwork (but it doesn't like all other multiplayer games).
The power of mods
But the best part is coming now: Mount & Blade uses python code and is pretty easy to script (not as easy as it could have been though) and right now many dozens of different mods have been released for the game. Some are historical simulations, others are just enhancements to the gameplay, others still change the game so it takes place in different settings like Star Wars and the Stone Ages. Sadly, some of the mods are somewhat amateurish. The Stone Age mod for example could use some work. But other mods like the Blood and Steel are very well made and additively entertaining to play.
If I were to rate the game solely on it's vanilla game and single-player only I would rate it 4/6 as a good game but thanks to the vast majority of mods and the inclusion of multiplayer this game deserves as much as 5/6, if the animations were a lot smoother and the controls wasn't that clunky the game would have been entitled a perfect score of 6/6 but sadly, there's some thing not even the mighty force of modders can solve. Also, if it could have incorporated some sort of co-op it would also have deserved the highest score...