I beat it too, 14 hours.
Well, that's the first part, though. In the first campaign, NPCs don't do anything. They just sit and wait while you build a team and conquer everywhere.
Once you've beaten the campaign, though, the other scenarios unlock, in which the NPCs actually do something. A lot of new options are also unlocked, so you have a lot more stuff you can do during your turns, and the game becomes a proper strategic game with the computers attacking and stealing your cities and whatnot.
I'd say the first campaign is a glorified tutorial for what's to come. Well worth it.
Also, to whoever said they had no idea how to play the game in japanese, there are enough icons to make up for it. They mostly tell you what they do, and if they don't you can just try them and figure it out.
Anyone knows if WoodR4 will get updated soon? I can't wait to play this with my brother.
O_O ...sound like... legit war sim... arghhh, must... not.. buy new DS...