It's a stronger book, it has more depth and it displays Fitzgerald's full literary talent. At the same time, it's not as "American" because the book deals with expats in Europe (loosely based on Fitzgerald's life, of course). Also, because it's more autobiographical I think that it may be difficult for some readers to enjoy - the descent into madness of Zelda Fitzgerald is on display, and to some it might seem like airing dirty laundry in public.
I would still rank it as Fitzgerald's best, followed by Gatsby, followed by This Side of Paradise, with The Beautiful and Damned as his weakest effort. I don't consider The Love of the Last Tycoon because it was unfinished at the time of his death.
ἡ δὲ κἀκ τριῶν τρυπημάτων ἐργαζομένη ἐνεκάλει τῇ φύσει, δυσφορουμένη, ὅτι δὴ μὴ καὶ τοὺς τιτθοὺς αὐτῇ εὐρύτερον ἢ νῦν εἰσι τρυπώη, ὅπως καὶ ἄλλην ἐνταῦθα μίξιν ἐπιτεχνᾶσθαι δυνατὴ εἴη. – Procopius
Ummaka qinnassa nīk!
*MySmiley*