It's an under-rated yet enjoyable game imo; not to mention it's a rather nishe game.
Beyond doujin games, you can't get more nishe than
when it comes to commercial games.I pretty much would call it a mash up game that have "iconic" characters such as "Disgaea"'s Etna and Prinny fighting alongside "Dark Stalkers" characters such as Felicia, Morrigan, Jedah among a couple of other characters from other games I don't even recognize a couple of characters from some of the other games
(Really Capcom I know of your generosity with your ip but wow, )
Seriously though this game is a huge hit or miss for anybody.
You will either love it or hate it; especially if you've never played games from the likes of NIS.
I actually would weigh against getting it if you're not used to nishe games that rarely push the graphical strength of current systems beyond PS2 standards (sometimes even bordering PS1 standards on certain static backgrounds for reason unknown to myself). In the combat segments you'll find yourself wondering why are the enemies either sprite animated ones, cg modeled ones, or even a combination of both.
I've wondered about that too...
However past all that I have to say I've enjoyed playing it and am glad to have it part of my PS3 library. Aside from the fan service, (whether it was avoidable or not is debatable, unless ya don't give a shit as it's for fun), the DLC that tries to nickel & dime you (The free ones are all that you should ever really bother getting I wouldn't bother with the charging ones imo), The game can be very cruel yet rewarding with its challenges and difficulty.
Essentially as most games of similar vein (Disgaea's inclusion, if only in its' characters, should be a huge red flag on this part) emphasizes on grandiose attacks, combos, spells, spell combos, ex-combos etc. Simply go DBZ/Fist of the North Star/Fist of an Angry God experiencing a GOD-TIERed ROID RAGE on the enemies.
Beats playing the next iteration of Madden/NBA/perhaps even Final Fantasy (at times and I love playing FF games) if you ask me...