I didn't really know Rob, having only met him a couple of times. And I haven't read all his novels - I've read neither Mythago Wood or Lavondyss, though the latter has sat on my shelves for a long time.
But Rob was my first guest when I officially took over as London Meetings Officer of the British Science Fiction Association. He was an excellent guest, interviewed by Paul Kincaid. We had a packed room, and everyone enjoyed it.
In preparation for this meeting, I had read Rob's then most recent series, The Merlin Codex. In this series, he mixes up two distinct legendary stories, those of Jason and Merlin. This brings a brilliant new twist to the often overly familiar Arthurian mythos, though Rob told me that this wasn't why he wrote the series - his original intention was to explore Jason and Medea, and Merlin was added later.
One should also mention Rob's non-fiction writing and his fan activity. Back in the 1970s he was a regular fixture at sf conventions. And one of my prize finds in my local bookshop was a copy of the Encyclopedia of Science Fiction, for the princely sum of 50p. Rob was consulting editor, which essentially meant he edited it. Overshadowed nowadays by the more famous Nicholls/Clute Encyclopedia, it's worth getting hold of, if you can. There's some excellent contributors, including Brian Stableford, Chris Priest, Harry Harrison and Malcolm Edwards.
I should have got Rob to sign it.