If you're not a fan of the Disgaea games of the past, you're not going to be any more impressed by this one. The story and many of the characters are new, but the game system and conventions are the same as they've always been. Fortunately, many of us are perfectly fine with that.
The new HD sprites are beautiful and make this feel like it actually belongs on the PS3, whereas D3 left me wondering. The storyline is excellent, filled with humor and mirth, with some serious undertones often hidden behind metaphors that, unless seriously considered, will likely fly over people's heads. Some of what Desco says, for instance, has meaning beyond her candor. I found the characters, for the most part, endearing and as colorful as the game, and have thoroughly enjoyed playing. For those of you who love powerleveling your character, Disgaea 4 makes it easier than ever with Evil Icons that allow you to share exp and Mana gain among your members, making it easier to open up those top-tier job classes than ever before.
If you love Disgaea, you'll love this. For those who just want a good tactics game, I recommend this as well; the powerleveling is icing on the cake, but thanks to the Senate system, you have the ability to control the level of the monsters you encounter and make it so you never have to do any powerleveling at all, if you chose to avoid it.