Tarantino strikes me as a prime example of someone whose work has suffered from his success.
Back when he was starting out, and still had to pay attention to criticism, he produced solid, well-structured work with a flair for dialogue and story construction, like Reservoir Dogs and Pulp Fiction. With the Kill Bill films and Inglorius Basterds (forgive me if that is not the correct mispelling), there is far too much self-indulgence. It seems there is no one willing to say to him, "That scene drags," or, "This sequence is all very well in itself, but it unbalances the narrative," or, "These actions are insufficiently motivated, " or, "You can't be serious about casting Eli Roth." Or, at least, no one who he'll listen too.
It seems to be a common problem. Stephen King's best books are his early ones, before he got too big to edit. J K Rowling's Harry Potter books just got more and more bloated. The worst episodes of Russell T Davies' run of Doctor Who were the ones he wrote himself.
A good editor should have a price above rubies.