They surely have some great hits but, in general, they ar pretty much worse than other rock groups formed in the sixties or seventies.
To start, Mick Jagger's voice is nothing more than normal, and that, my friend, is one of the most important and characteristic aspects to be taken into account about any band. For his credit, it's very personal and different, and that makes the whole group different, but that's not enough.
And about the instrumental part, it's just ok, 'cause in many songs the melody is almost absent, and personally I think that's one of the things that makes great a song.