Yeah, I was really disappointed when I saw Nintendo Power give it a 5/10, but to be fair, they also gave Dark Spire a 5/10, which is one of the finest, old school dungeon crawlers in years. It's a shame that a lot of people are going to pass these games up based on those reviews.
I bought it and I'm not a "devoted" fan (I've only played a few hours of Earthbound and that's it). I bought it because I'm a huge RPG fan and was impressed/stunned by how beautiful the guide looked. And maybe one day I'll find the time to actually play the mother games and become a fan. :)