Samurai Warriors 3
Stupidly large amount of content
Variable missions and huge and distinct playable cast
Really hard game in the harder difficulties, but perfectly playable in standard and/or easy
Everything had co-op
In addition to everything, the game even had a (limited) character creator, including appearance and a campaign mode just for those characters.
I just loved the game, but reviews we very harsh and plainly lies at times.
Yes, the minor enemies don't attack much playing on normal, but then just go on hard or worse and even the peons will start poking the player all the time if you get in their range. Then there's also the very different gameplay structure of the Murasama Castle mode, which makes the game play more like a standard action game, without the focus on the army units, conquering gates and objectives in general (well, aside from a bunch of escort missions).
The game does have problems though, like the framerate and the graphics really aren't good, but that's not nearly enough for the negative reception it had from most reviewers.