GRRM is a deft storyteller, a wonderfully subtle character writer, and a mostly mediocre stylist. Even with better editing, ASOIAF wouldn't have much literary merit. The prose is very sloppy. Lots of awkward and probably unintentional repetition of words like "ponderous"—whole phrases too.
Stylistic quirks are pardonable until their accretion becomes distracting, as GRRM's has since the very first book in the series. It's sad to have to say, because GRRM is so clearly capable of better. There are picturesque phrases scattered throughout ASOIAF. Some chapters have real poetic force. If only he could maintain that quality with something approaching consistency, he might just deserve to be favored with those Tolkien comparisons that overenthused reviewers like to make.
Literature or not, the series is shaping up to be an influential work in fantasy and a major accomplishment in its own right. GRRM's world is sufficiently compelling to be remembered alongside Harry Potter. I honestly don't think I'm damning him with faint praise here; it's not easy to create a distinctive original universe with characters and places and events that are complex enough to be interesting yet coherent enough to sustain interest and withstand intense scrutiny from invested fans.
If you want to read some undeniably literary genre fiction, try Gene Wolfe's
The Fifth Head of Cerberus, The Book of the New Sun (
Pt. 1 and
Pt. 2), and it sequel,
The Urth of the New Sun.