I have to say, I've gotten some great mileage out of this game already and am looking forward to more.
Being a fan of the developer thanks to interesting RPGs like Persona 3 and Riviera I was looking forward to this game, so much so that I actually picked it up the day it came out, roped in three buddies and began our epic quest. I was very glad to add another game to the (embarassingly short) list of Wii games my friends and I would deign to play for more than a round or two.
Together we dove straight into the campaign mode and since then every night we found all our players free we'd end up playing the game into the wee hours of the morning. Between the over-the-top battle maneuvers, the interesting classes and abilities to chose from, and the often ludicrous missions presented in such a way that we have yet to have our interest waver... It was exciting and interesting to witness the new events and explore each new area thoroughly, whenever we weren't laughing our asses off at the heaps of satirical humor found in almost every aspect of the game.
I don't have much to say about any other game mode, however. We tried playing a 'battle' game with a couple new friends once and found the inability to scale the length of the game and lack of exploration or variation really killed our enjoyment of the game... It really does seem like you should play this game for the campaign mode or not at all. Being able to set absent players to NPC mid-game was also very convenient, allowing us to play when we were down a man if they didn't mind too terribly. It has its flaws, like any game, but it really comes down to what you want from it.
It's definitely not a game for everyone, but if you have some RPG gamers looking for a fun party game, then I think you'll definitely dig Dokapon Kingdom. This is just my personal opinion... but really, you can do a whole lot worse on the Wii.