Darth mod establishes a number of more realistic formations for the AI forces. Since AI "tactics" are influenced by formation choices, the net result is a slightly tougher opponent (and a more realistic one).

E.G.

In vanilla, a 19-card barbarian army very often tried to deploy in an extended line of 16 units with a couple flanking the general on a second line in the center. This formation was unwieldy and unrealistic. You could refuse both of your flanks and punch through the center or any of a number of easy counters. It looked impressive and you would certainly be flanked, but it had no reserves or depth -- no punch.

In Darth mod, they'll often take a sort of 3-4 deep pair of columns and bring in swarms of axemen on a single target. Much more of a threat.