IMO Its a good game. I played it for over 50hrs to unlock everything. Its a little mindless hack n slash with some strategy and RPG elements thrown in. Its about 13 stages long with alternates of each stage after you get to a certain point. Its probably semi short if you rush through it, but your going to have a tougher time that way.
The cool thing about the game are that the legions you level up to a certain point give your character abilities even when not equiped. So, if you max out all legions in a certain attribute the main character is going to be the biggest ass kicker in the game other than the hidden legion. You also unlock a hidden character after you beat it. Which plays completely different than the main guy.
Anyway, if you like leveling up a few Legions, getting a powerful character, swarms of enemies attacking you, and you just hacking them up alone or with a few legions to help then this is the game for you. If not just ignore it and move along.
-Morpheus