For the longest time I couldn't really get into his work, thought it was far too preachy and annoying. But honestly, the more I read and the more time passes, the more I find myself agreeing with him. I still think he's preachy as fuck but even when I'm not on his side I really appreciate that he's putting so much effort into saying something with his work while also having fun.
Favorite stories off the top of my head are Nemesis the Warlock, Sláine, Charley's War and Marshal Law. I'd actually read Law years ago and didn't think much of it, but I revisited last year and loved it.
Also, I've been listening to his audiobook these last couple of weeks. It's scatterbrained as all fuck and a bit redundant but still really entertaining and insightful.>tfw Mills had a launch party for Requiem in France where he and Ledroit emerged from coffins surrounded by Claudia and Requiem cosplayers