Back in the early 90s Square didn't have a very high opinion of the US video gamer. They released a feature-light and easier version of Final Fantasy IV in the US and were disappointed with the sales numbers compared to the sales in Japan. They decided this was because the US gamer couldn't handle the length and slow pace of a JRPG and decided to make a gateway RPG to help ease them into the genre. So they took two development teams and set them each on their way to make the next Final Fantasy game. The team that did the first four Final Fantasy's went to work on Final Fantasy V. The team that did Final Fantasy Legend III set to work making the beginner RPG: Final Fantasy Mystic Quest. It was released in Japan as Final Fantasy USA and in Europe as Mystic Quest Legend. (Because Final Fantasy Adventure was release as Mystic Quest in Europe.)
The game gets pretty terrible reviews. It isn't uncommon to see people refer to it as the worst Final Fantasy game of all time. It's short and simple. It has aspects of an action-adventure game (no random encounters, you use your weapons to clear out obstacles and such like in Zelda).
When I was a kid I liked the game. I didn't own many games but my brother and I used to rent games constantly from video stores. Getting Final Fantasy IV for a weekend and having to share the SNES really meant not getting very far in the game. Final Fantasy Mystic Quest, on the other hand, was short enough that we made real progress. It was also easy enough that dying wasn't really an option (which meant it could stay my turn for HOURS at a time)! Sure, the story wasn't great (I actually don't remember anything about it so it certainly wasn't memorable) but I still got to see the whole thing.
When compared to other SNES RPGs I suspect it actually fares pretty well. It's just when compared to Final Fantasy IV and Final Fantasy VI that it really pales. I think the biggest strike against Mystic Quest is that Square didn't give us Final Fantasy V because they were trying to hook us up with Mystic Quest. On the plus side I think the fact that Mystic Quest ended up bombing as badly as it did prompted Square to give us Final Fantasy VI which was absolutely incredible.
I suspect it won't take me very long to get through this game. Not because I really want to play the game again (though I do want to give it another spin) but because the next four games in the marathon are V, VI, VII, and Tactics. Holy cow. (The only obstacle in the way would be if Blizzard manages to get the Diablo III servers to stay up constantly!)