Mount and Blade is initially kind of confusing when you're looking at it from the outside. What is this game, exactly? Is it just an open-world sandbox fantasy RPG like the Elder Scrolls games? But there's something about managing armies -- so is it like Dynasty Warriors then, where you take to the field of combat personally while also directing the troops around you?
The easy answer is "a little of both, plus some other stuff." It's fair to just call M&B a Skyrim-like WRPG, as you can certainly play it that way if you care to. You roll a character, fiddle with their stats, and then you can go around taking quests from lords and guildmasters or competing in arena battles for money and glory. But really, at its core, M&B shares most of its structure with the classic exploration-trade hybrid strategy-action games like Pirates!, Uncharted Waters and Elite. Games where you're basically turned loose on an open world to make money and survive however you care to, with no restriction on where you can go and what you can do other than your relative state of weakness and lack of funds at the very beginning.
One key difference here, though. While those other games largely let you roam as you pleased, they had some sort of overarching story or goal that you could return to and advance in chunks when you cared to. M&B has nothing like that. It has utterly no greater goal whatsoever. You entirely make your own story for yourself, and the game only ends when you get tired of it.
Some people need structure and direction in their games. Concrete objectives. They should probably stay clear of this one, as your goals are entirely self-determined here. There are some optional tasks with structure that you can get into, like pledging your service as a warrior (and eventually a commander) to one of the existing kingdoms, or finding disenfranchised claimants to those kingdoms and pitching in your lot with them in their very uphill battle to overthrow the current ruler. You can even eventually get your own lands granted to you by kings that you serve, which you then have to defend and tend to, and can also opt to start a rebellion and form your own faction. There is no "right choice" or "main quest branch" here, though -- you just pick the activity that sounds most appealing to you, and off you go.
While there is a simple trade system reminiscent of Uncharted Waters (find out where stuff is being sold cheaper than normal, haul all you can carry to where it is sold for more than normal without getting robbed en route), the game heavily centers on combat activities. The action-based combat system is simple, but effective, with the only weakness being that even the supposed higher-end AI fighters are pretty dumb and are only a threat when they swarm and overwhelm you in huge numbers.
Uncharted Waters and Pirates! are two of my most favorite games ever, so I do appreciate what the designers were going for here. That said, I do think the game could have stood just a *little* bit more structure and guidance right at the outset. You don't know, for example, that taking the first job in a village near your starting point training the villagers to repel bandits will lead you to get crushed by a heavily armed mounted cavalry. There are also certain lands where it's vital to recruit a good-size squad of companions, or the constantly roaming packs of bandits will crush you. Something like the early optional guidance you get from Caius Cosades in Morrowind probably would have been a good idea here.
If you don't mind unstructured play, and you're OK with some trial-and-error and unfair deaths at the outset to learn the game's quirks, however, this is really quite enjoyable. To me, this game is like if Conan decided not to even bother hunting down the James Earl Jones snake cult after he escaped and just decided to make his way in the world as a freebooting mercenary. It even has an epic symphonic soundtrack that's a bit Basil Poledouris-y to lend it that atmosphere (along with all the crazy shirtless hipsters and hobos you constantly have to cut down). You'll have the most fun if you approach it that way, as it so heavily centers on combat and doesn't have the alternate builds that focus on trading, conversation etc. that some other fantasy RPGs have. Roll up a hulking berzerker and split some skulls for its own sake, that's the way to do Mount & Blade.
* Great beginners guide
-- though I don't know why it has to be in some huge image format instead of a document
* Game of Thrones Mod
- Supposed to be excellent