Hows it going

[Ludens]

Have a look at the Engineer's Guild. All major M:TW modifications have a thread or forum there. Are you looking for a more challenging medieval game or do you want a total conversion?

Welcome to the Org, BTW .

[Quintus Of Pompeii]

Hi There

[Martok]

As Ludens indicated, it depends on what exactly you're looking for. If you want a mod that expands/refines on the medieval setting, then I would recommend VikingHorde's XL Mod, BKB's Super Mod, and/or Wes' MedMod. All three are excellent add-ons to MTW/VI, enhancing the original gameplay significantly.

If you're looking for a "total conversion" mod (so called for going with a different setting/time period entirely), then probably the foremost of these are Hellenic Total War, Pike & Musket TW, and Samurai Warlords. All three of these mods can be found here.

In addition to all these, there are also more mods available in the Engineers Guild. Have fun, and good luck!