The thing that stands out the most is the characters. They have somewhat cliché exteriors, but there are quite complex personalities and motivations lurking underneath that get revealed as the manga goes along, especially the leads. I was particularly impressed with Tohru, I never thought that your average anime/manga ditz could be so interesting. The main plot is also very interesting, with themes of love, loss and redemption. It's very sweet, and I really liked the ending.
There is a very large cast, 3 main leads and at least 15 supporting and assorted minor characters (that's off the top of my head, there's probably more). Natsuki Takaya does a marvellous job of giving every character a decent amount of time, each with a backstory and secondary plot that gets resolved.....I can't think of one that didn't get resolved in a manner I did not like. There were occasions that the story did make the happy to sad transition rather quickly that it was a little jarring, but on the whole the jokes and serious stuff are quite well balanced out. A couple of the plot devices did feel a little contrived, but they didn't look out of place.
But having such a large cast means that it can be difficult to follow what's happening to or with who, and it isn't helped by the fact that some of the character designs are very similar. There were quite a few occasions where I had to do a double take (like 'how the hell does Kimi know Rin?....Oh, wait, that's Kagura). But on the whole, I did like the art. Natsuki Takaya gets better as the series goes along, and she does a good job of changing her characters as they grow older.
I think I would reccomend Fruits Basket to just about anybody. I think it has something to offer to everyone, not just a romance story.
