A Clash of Kings is good if hard, there is also another ASOIF mod called A World of Ice and Fire
last days of the third age if you enjoy Lord of the Rings, has loads of pretty nifty scriping and gives you an overall campaign to fight and win in. some bullshit RNG where you can permanently lose stats tho.
Prophesy of Pendor is pretty fun, includes a custom system where you can build your own knight orders and train up members a la companions, good for padding out your late game armies.
Perisno is fun, a very Warhammer inspired fantasy world with very stereotypical but fun factions
Gekokujo if you want some Japanese warlordism, there are loads of blends between it and the diplomacy mod kicking around on 4chan's /vg/ thread for mount and blade