Mordheim does to Warhammer Fantasy what Necromunda does to Warhammer 40k. The game mechanics work in classic Games Workshop fashion.
Instead of playing with hundreds of miniatures, you pick a warband of 1-20 models (most average at 10-12 or so), and fight a skirmish with other warbands. If you play well, your warband gains money, levels, size, and new powers, but play badly and your warband slowly deteriorates as people die or otherwise get dismembered.
Games actually play very similar to Necromunda but due to the fantasy setting you should see fewer long distance shots, and a lot more hand to hand fighting.