Coming from someone who usually reads more gory, twisted stuff, I gotta say, this is one of the best mangas I've read lately. While I couldn't give it perfect tens all across, it is DEFINITELY a great manga, especially to someone who's new to it. And here are some breif reasons why.
1.) The overall story. While the plot is sort of shojo-cliche (average school girl ets sucked into different world and given a great responsibility), it has a lot of good twists. Like, REALLY good. I would find myself thinking "wow...that was stupid..." and then reading on to realize that whatever happened was actually important. A few parts still revert back to cliche shojoness, but overall, the storyline is riveting and unique.
2.) The character development and relationships. I actually connected to them really well. They were cute and quirky and all had interesting stories behind them. Many of them had very interesting, fickle personalities that made me love and hate them at the same time. And the romance between the two main characters is a very simple, but still cute. Not to mention, the characters manage to be serious, but still have some comic relief added to them at times. They're all very likeable, and you feel like you would have fun hanging out with them.
3.) The ART. OMG. THE ART. Those who really know the manga world know Yuu Watase, the author/artist. Overall, I think that she's better at art. But seriously...she's better than a whole freaking lot of people at that. I really like how she can draw the sexiest bishies known to mankind, and also something really really REALLY ugly (those of you who know of the Darva monster from Alive 19th? Um...yeah...). She has great attention to details, and dressing characters according to their personalities. All in all...even if her drawing style isn't the most unique and out-there, it's really pretty.

SO YEAH. This was a solid manga that I would recommend mainly to girls, seeing as it is shojo. But no matter what your taste, I think you can find something to enjoy in Fushigi Yugi.