He is great, indeed, though more for what he opened up (not just to Debussy, Ravel, Poulenc and the Arceuil school but also, even, to John Cage, who he influenced deeply), than for his music. There are, probably, only a few really, truly strong pieces (Socrate, the Nocturnes, Sports et Divertissements, Pieces en forme de poire, and actually the famous earlier pieces too - Gymnopedies, Gnossiennes, Sarabandes). However, I wouldn't willingly exchange these ones for anything.
He's a fascinating figure, much misunderstood, and admirable on a personal level in so many ways (witness his going back to the conservatoire in all humility at a late age; in general witness the strength of character that enabled him to live the life he did, isolated in Arceuil). Also among the most anecdote-ridden of composers! Get hold of Rollo Myers' old biography. It's the only one I've read, it may be superceded by later ones, but it comes from very close to the source and feels genuine and passionate.