I really don't see what the big deal with Disgaea is; personally I think it's overrated due to how semi-tough it is to find.
I have it and have put around 30 hours into it. I have several problems with the game. First, you only gain EXP when you kill an enemy. I liked FFT's system for EXP a lot better. In Disgaea, this setup single-handedly led me to have a really powerful Laharl and nobody else in my crew really being worth a damn.
The character class system is alright, but FFT's was way better since you could switch jobs without "transmigrating" your character. Transmigrating is a cool idea, but it takes a lot of time. Which brings me to one of my big complaints:
Most cool, unique features of this game are only that great if you plan on putting 100+ hours into it. You can level up to 999! You can go through the item world for EVERY SINGLE ITEM! Great, but holy crap, who actually does all that? I have little room to talk, being an avid gamer, but jeez. If you're actually doing all this, please, get up, go outside and contribute to society in some way.
I mean, I guess if you only had to own one game or something, Disgaea would be cool since it has so much to do. I just feel like it's gimmicky, overrated, and doesn't begin to approach the greatness that was FFT. And the storyline was alright, pretty humorous, but certainly not gripping or serious in any way. If you're an anime fan, which I'm not, you might dig it.
For all I've said, don't get me wrong, I LIKE Disgaea. I just don't see the big deal; I'd probably give it around a 7/10.