I realize the Mother series is a fantastic series, in fact, I've heard Mother 3 was an amazing game, but Monster Hunter is nothing to be disappointed about. And considering that Nintendo has no plans to continue the Mother series, I'd much rather get my hand on a Monster Hunter game in the US.
I currently have 75 hours clocked into Monster Hunter Tri. (I would have more, but I kinda lost my skill after taking a break, LOL.) What I like about the games is that it isn't a generic MMO type game. Hunting these monsters takes skill which is severely lacking in these types of games lately. Memorizing monster patterns, and taking one down with a group of friends is awesome.