I'll also vouch for M&B warband - a great game, if a little rough around the edges.
My favourite thing about it is the combat. The story is non-existent - basically you make your own, although you do get some standard quests and plenty of scope to do things (i.e. become a lord/have your own kingdom). The graphics are decent enough for me to enjoy but aren't great compared to most modern games. The sound is decent (the quests aren't voiced though).
The combat though - you've got melee combat (with parrying, shields etc.), mounted combat (with lances), and ranged combat, all of which are very well done, and really help immerse you in the game.
Your character can specialise in whatever they want, so you could focus on being great at all three of the above, or sacrifice them for skills to support any troops you command.
I've never spent too long with the army/troop aspect in terms of battle commands (they're fairly limited although you do still have some options), but the troops are also a well done part of the game, with each individual soldier gaining experience and being able to be promoted to a more advanced unit.
You can also then have a few followers who operate on the same progression as you (i.e. you can choose how to upgrade their skills and equipment, compared to a standard troop unit where you choose between pre-set upgrades).
There's also multiplayer which is a bit hit and miss but can be OK - it's essentially a medieval RPG-lite counterstrike with sieges instead of demolition maps.
This is also all before you consider the various mods out there - I've only tried one myself but there are plenty to choose from, and either enhance the original game or give you an entirely different setting.