Easy to learn, hard to master...
For instance: graphics... Players who know Nippon Ichi know that they prefer gameplay over graphics. This shows. The backgrounds are great, worthy of Playstation 3, the characters and monsters in the game however are still simple 2d sprites, which I think is a great decision. Why would anyone like to see a 3d version of Laharl or Etna or any other character? The retro vibe they give in their current look is just great. In the end though I think most players would be a bit disappointed that Nippon Ichi did not make more of an effort to get more out of the PS3's capacities.
The music and sound effects as well as the voice acting in the game either strike you as charming and fitting to this game or as bloody annoying. Thankfully though, you can pick the song you want to hear eventually and switch between English and Japanese voice acting. Both are excellent in my opinion.
The story of Disgaea 3 isn't the usual RPG epic save the world or universe from the ominous threatening demon / power driven madman / insane scientist or whatever. It breaks down as a simple though very enjoyable story about a student demon who wants to take revenge on his dad, the overlord for trampling his Slaystation with over 4 billion hours of savegames on them. (major plot twists and surprises ahead.) The story unfolds in a charming way, with a lot of humor that we got accustomed to since the very first installment of Disgaea on Playstation 2.
To describe the gameplay in one paragraph would not exactly do justice to this game, because there is just so much to do... Level your characters to insane heights (level 9999, no typo!), unlock new and hidden moves, unlock new character classes, improve your weapons, 8 different endings to obtain, which require you to try a lot of different playstyles throughout the game. (if all else fails, try losing...) And let's not forget about all the post game stuff to unlock, like extra playable heroes from other Nippon Ichi titles and a face off with the legendary overlord himself; eater of worlds, destroyer of universes; Baal! This all provides a great replay value for this game.
Newcomers to this game will almost surely feel overwhelmed by the sheer possibilities of this game. Fortunately there are a lot of players active on the Gamespot forums who are willing to help you tweek your performance and get you where you want to be in no time.
All in all I think this game is almost a perfect example of what turn based strategy should be like. Minor flaws like the absence of trophies and the dated / retro graphics should not keep you from playing this game if you're a fan of the genre. If you're not familiar with the genre, this is the best game to try if it suits you. Do not let the overwhelming content keep you away from this pearl of a game. This game deserves to be played hundreds of hours...