In the first Disgaea, you had to go to the Dark Assembly in between battles to ask for more troops. Same thing applies here - if you want powerful units, the senators have to approve drafting such a potentially dangerous ally. If they're not really fond of you, they'll strike your proposal down, so, you've got to bribe, booze or blast your way into their hearts.
The Dark Court, on the other hand, is all about contradictory behavior. The more times you pull off cheap shots in battle, or level up too much, or whatever the situation may be, you're called to court, where the guilty are rewarded. Demons wear felonies like trophies, but go too far and even these judges will crack and hand down some punishment.
The new stacking ability (piling units on top of each other for a vertical-gauntlet kind of attack) lets you pour on the pain, but you can coast through most of the game without relying on it. But, this is a personal choice, just like the armies you can craft, so each player will find different uses for stacking, recruiting troops and summoning them onto the battle map.
It would be nice if the bottomless Item World weren't the primary way to level up your weapons. Most of the time, the stores don't sell the best stuff - you've got to literally head inside the item in question, tear through its series of monster-ridden floors and gain attributes for each area cleared. Not a bad way to lengthen the game, but annoying when you just want a new axe, dammit.