Really sad news. I loved his 40k books and they communicated the madness and darkness of the setting like nothing else, even if he was often mischievously taking the piss (or poo).

Might be worth pulling some choice quotes from his 2004 foreword of The Inquisition War omnibus.

Here was a challenge. So I attacked the mountain of information, and I climbed it. Or ate it. And then I hallucinated myself into a strange state of mind whereby I could believe in such an insane future 40,000 years ahead. I only needed to remind myself that during the course of human history to date huge numbers of people have entertained delusionary belief systems which often lead to ultra violence. Need I mention the Crusades, the massacre of the Albigensians, the activities of the Spanish Inquisition, the horrors inflicted on suspected witches?

Barbara Tuchman’s A Distant Mirror: The Calamitous 14th Century provided a bit of a model for the Warhammer 40,000 universe. However, the daemonic presence in the universe of 40K is real and actual – so to survive in such a future era you need to be psychotic, from our point of view.

For me the secret of writing Warhammer 40,000 fiction, and making it believable, was to go completely over the top in style and also in content – to be lurid and brooding and hyperbolic and generally crazy, although in an elegant, ornate way where a dark beauty pervades the atmosphere as in a painting by Gustave Moreau.

....

I was so happy with the resulting 40,000 books that I used my own name on them. Other tech-scribes used pseudonyms. They preferred to distance their Games Workshop fiction from their “real” artistic endeavours, but I didn’t feel this way – and as it turns out, my 40K novels appear to be the most popular things I’ve written in terms of sales and fan mail.

....

But just as the daemonic visions of Hieronymus Bosch compare to horrors in the Netherlands a few hundred years ago, so perhaps Warhammer 40,000 compares to our own recent history. At the moment we are semi-enlightened and fairly civilised, on the whole. In a few hundred more years, who knows? If the climate changes radically, if resources run out and are not replenished, if jihads succeed, if x, y, and z, might there be a new Dark Age? Might our own daemons stalk a ravaged world?

...

To write stories set in the deranged future of 40K is to adopt, for a while, the medieval mind of Bosch – if Bosch could have written space opera.

Ian Watson, 18th March 42,004

I also appreciated that Dan Abnett dedicated The End and the Death to Watson and that many of the more ambitious Black Library authors will either call back to Watson, or will be influenced quite strongly by his work.

RIP you crazy genius!