I'm usually quite hostile to criticism of Tolkein - although I'm not a massive fan of the Big T, I think most criticism is ignorant and prejudiced. It's usually in the context of 'mimesis is the only standard of quality' or some such bollocks.
Instead Mieville criticises while he lauds Tolkein's achievement:
Tolkien is an outsider artist. His genius lay in his neurotic, self-contained, paranoid creation of a secondary world. That act of profoundly radical geekery reversed the hitherto-existing fantasy subcreation: Middle Earth comes before the stories that occur within it. It’s precisely this approach, the subject of most scorn from the ‘mainstream’, which is Tolkien’s most truly radical and seminal moment.
And he addresses - in JRRTs favour - the difference between fantasy as allegory (spew) and fantasy as metaphor (hurrah).
Tolkien’s ‘cordial dislike’ of allegory does not, as some of his followers, most of his detractors, and the man himself seems to think, imply a fiction divorced from reality – a fiction ‘about’ nothing real. What it means is a fantasy that is not reducible to a kind of philistine, simplistic, moralising, fabular representation of soi-disant ‘meaningful’ concerns, as with fiction that despises its own fantastic. Dispensing with allegory cannot mean dispensing with metaphor: fantasy that believes itself is about itself and also about other things.
That's an excellent summation of what is good about fantasy. He liked Sean Bean too.
it's also worth scrolling down to footnote 11, in minuscule typeface, with an extended discussion of M John Harrison, which seems very shrewd to me. 'for MJH … this is at the heart of fantasy and escapism – the idea that we can somehow transform ourselves completely, and make everything alright… But in the moment that we reach out for what we desire, what is going to change us, it slips away. … Fantasy is a sort of fetishization of the moment of choice when everything seems possible…'