All these pages but no one has mentioned the short stories?
Dreaming is a Private Thing, The Ugly Little Boy, The Last Question, The Feeling of Power, The Martian Way, his short stories do include bad pulp like Friars but there is an impressive body of work there. The notion that Asimov isn't a "character driven" writer is exposed as the canard it really is. At least, in any reasonable interpretation of "character driven," which sometimes is code for some unsavory fantasies held by the (mis)user of the phrase.
Sometimes it seems to me that the real heart of science fiction is the short story. Possibly that's because short stories seem to have been peculiarly important in US literature, from the days of Washington Irving to Edgar Allan Poe and Nathaniel Hawthorne. Just looking at the novels is very misleading I think.
I think the best short story collections, aside from I, Robot and Foundation (using "short story" a little loosely there,) are Earth is Room Enough and Nine Tomorrows.
As to comparisons with Clarke and Heinlein, looking at the short stories, Heinlein does indeed bring up the rear, even remembering All You Zombies or By His Bootstraps. Heinlein's literary reputation I think in the end will rest upon the juveniles and the adult novels Double Star and The Door into Summer.
Stranger in a Strange Land will be remembered as a succes de scandale (pardon my French.) When conservatism becomes unfashionable again, Starship Troopers will die, while Farnham's Freehold and the brain transplant one that seems to be devoted to rationalizing sexual fantasies might kill his reputation despite the juveniles.
The day will not be soon. As noted, there is a two volume hagiography coming out. It is poor, poor stuff. It doesn't even wonder about the finances of Heinlein's silver mining venture. In discussing Heinlein's involvement in Upton Sinclair's EPIC campaign, it quotes Heinlein as talking about secret meetings of the Communist Party or about his factionalizing with EPIC without wondering what intelligence (military or police,) and business contacts Heinlein had when he was supposedly working for Sinclair!
On the subject of science fiction writers of stature, the truth of course is that H.G. Wells was and remains a writer of enormous stature. He is not considered so in conventional wisdom for political reasons and because it just offends against the canons of literature to imagine that things will be different, instead of plumbing the depths (yet again) of eternal Human Nature.