So I picked up Children of Mana this weekend; got one copy for me and one copy for my girlfriend. We played like 6 hours straight, and I can definitely see how this would get very old, very fast in single-player mode.
But I must say, if you've got two or more people playing together, it's an absolute blast. It's a button-mashing dungeon-crawler, period. It's also got some design flaws (for example, all the quests are pretty much the same: clear dungeon of enemies to complete the quest) and magic is pretty much useless so far (which eliminates being the magic-based character).
Still, it's got that PSO-style addictiveness to it in that it's kind of a crappy game at heart, but so much fun to play and impossible to put down, given you have friends who also own it. I can't recommend it, but under the right circumstances, there is enjoyment to be had here.
Music is also very kickass.