I'd suggest "Phantom Brave" on PSP. In terms of presentation, it has the same art style as Disgaea, but trades the humour for a serious and occasionally darker tone. It's an SRPG, but without a grid, and your main character, Marona, sends out characters that last a short time before they expire. Marona and the rest of your characters that you create can equip any item, from a fish to a sword to another character (yours or the opposition), and use any skill that they or their item knows.
Levelling is just as multifaceted - you can increase a character's level, increase the stat of titles which are equipped to characters, improve and modify the items a character equips, create and raise new characters, and reincarnate old characters too.
There's a great deal of stuff to get the most out of the game, like all NIS games, and lots of exploits to learn, but then again, that's what makes NIS games so much fun.
Outside of Disgaea, my favorite NIS game has to be Makai Kingdom. That game had amazing gameplay, fantastic music, lovable characters, hilarious dialogue and brought some elements to the table that i would love to see in another NIS game.
Unlike some of the other NIS games, Makai Kingdom made me feel like I really was an Overlord managing my own Demonic Army (complete with Vehicles and Buildings to boot). Whether I was on the battlefield fighting enemy soldiers, horrible monsters and mutant vegetables or just chilling in my kingdom talking to my troops, I was having a blast with Makai Kingdom. If you can get a copy, i highly recommend it.
"I just beat Mag-Freaking-Neto! Where yo curly mustache at?!" - Deadpool "I reject your reality and substitute my own" - Adam Savage