Recently finished the Starfish quadrilogy and adored it as well. One thing I particularly like is how this theme of evolutionary pressure applies to everyone alike; characters, software, ideologies, neural nets.
Also Watts manages to conjure this feeling of future shock I've only previously felt with Charles Stross' work.
Honestly, I thought the Behemoth pair dragged a bit - I suspect it might have worked better as a more tightly-edited single volume.
(Sue Burke's Semiosis trilogy is worth a read, too, in a similar evolutionary SF vein.)