Disgaea 2 is Disgaea 1 with a slightly worse story, but more solid gameplay
The gameplay mechanics have been redone and polished. The animations are even more fluid before. Character design is unique as usual, and dialogue is sharp and funny. Disgaea 2 is faithful to its original game as well, and contains many appreciated cameos and character choices.
All in all, Disgaea 2 is a great game, but not quite..an epic game. This is because Disgaea 2's storyline suffers from being worse than its predecessor. And though this may be a bit unfair of a comparison because Disgaea had one of the most epic storylines of all sRPG-time, the fact still remains. The characters and story in Disgaea 1 were more involved and impressive, and thus D2 has to suffer for its older brother's accomplishments.
Still, despite this fact, the game is great overall. The story is not epic, but by no means bad. In fact, its pretty good. And same goes to the characters. In addition, hands down, the battle system is better and more slick..so slick, that playing Disgaea 1 again might not feel as good anymore, because of all the numerous improvements