Well, that's definitely overrating. There is no way you can compare a show, and I quote the great Ian McShane here, with tits and dragons, to masterpieces like The Wire or The Sopranos, or even something like Mad Men.
I also think it's underrating it to say it wasn't, at its peak, one of TV's great shows. Season's one to four were excellent and the show itself should be remembered for making television a valid space for having movie-esque budgets and battles. Without GoT I don't think we'd be seeing some of the other big budget shows we are now.
So yeah, the answer probably lies somewhere in the middle, season's 1-4, and parts of 5 and 6 should be remembered as top 10 or 20 TV, but it was never anything close to the "best".