The normal 1257 AD mod is set in Calradia, with the "usual" factions. The 1257 AD Middle Europe sub-mod (there's a thread for it a ways down the 1257 mod forum, and M&B Nexus still has the download) uses historical factions (Austria, Russia, Poland, Hungary, Bohemia) on a ginormous map (loosely based in reality).
The main reason to play Lords and Realms would be the kingdom management aspect. Several other mods have incorporated those same kingdom features:
Sword of Damocles goes a step further yet, including laws that affect taxes and relations with different "classes" within your kingdom, and requires certain buildings to advance some troop types. Once again, the vanilla content is mostly eclipsed by the mod content, and gaining that first castle to upgrade your troops can be extremely situational and luck-dependent. Until then, you're stuck using mostly bottom-rung fodder, and trying to find faction castles where they will allow you to upgrade one or two specific troops types. There's one nasty bug that almost inevitably results in every other faction eventually declaring war on you, since Universities, which are supposed to gradually remove your bad reputation due to taking castles and towns, end up increasing it instead. After a while, the AI builds Universities in its towns, so if/when you take more than 1 or 2 of them, you become increasingly hated by all. I've never gotten past that point, and the mod is essentially long dead, so no fix is ever likely.
The Eagle and the Wolves is set in Arthurian Britain, and allows you to run your own kingdom. Balance is somewhere between vanilla and those "uber" mods. I've played it quite a bit, and my main gripe is that the Roman remnant has intentionally been short-changed with sub-par units, even at the top tier (historically, the "soft" Romans took a bit more work to "harden" into battle-worthy troops, but once that was done, they were every bit as effective as their competitors).
Custom Settlements allows you to build up your own settlement from an empty plot of land (in pre-placed locations), but the mod is still very unfinished; good idea, but only semi-playable. For instance, about half of the settlement locations are named "Emp-something-or-other", like Emptoor, Empstead, Emp43, etc. That "EMP" beginning means that it has not been completed, and isn't playable (some will crash the game, or leave you and your army stuck at the edge of the map).
Star Wars Conquest includes some kingdom features, and if you haven't tried it, it's worth checking out, if for no other reason than to see just how much can be done with the M&B engine. It's a pretty impressive overhaul, yet a lot of the basic M&B functions are still recognizable "under the hood" (Speeder bikes are massively reskinned "horses", force powers are handled as "weapons" and "shields", movement on the map and various party skills can be "enhanced" by buying different ships, etc.). The dialog still has some very out-of-place remnants as well (I actually spent the better part of a couple weekends altering some of them, with mixed success).
