Disgaea is a well-polished and deep strategy RPG, though it's for true strategy RPG gamers only!
The characters and their voice-overs are well done, the cutscenes are cute and funny, and the story is surprisingly engaging.
That all said, unless you are 100% a strategy RPG nut, you will NOT like this game. The game's entire value comes from the strategic semi-traditional grid-based battles. There's a lot of "level grinding" to be done, and to do that, you'll be playing lots of very similar battles many, many times. However, for strategy RPG fans, Disgaea offers a lot of fun and unique twists throughout (I won't spoil it for you, but it's more than your usual mix of melee, magic, and ranged combat.)
So if you're looking for the next Final Fantasy Crisis Core, keep looking. If you're looking for a terrific SRPG, this is an excellent choice. There's a HUGE amount of replayability, through unlockables, additional enemies and a lot of little tid-bits to discover. You just need the patience and love of the genre to get there.