(side note: It's been a while since I've read them, and I admit I generally only reread the first 4 or so, due to sameiness and/or IMB's increasingly grody enthusiasm to describe Bad Stuff happening to people, preferably women, so we can be really righteously mad when There is Big Revenge. Sadly, this enthusiasm seems to have sparked a trend among even less-restrained authors like Richard Morgan, so I often hesitate to pick up an SF book for fear of reading about, I dunno, women getting heated irons stuffed into their genitals or something)
That said, Contact and Special Circumstances are usually what he describes - it's like he couldn't quite come up with much to write about that was within the Culture per se. So most of the action is the Culture at war, regardless of how supposedly peaceful and enlightened the Culture is.
I'm not surprised that Bezos and Musk are fans. Given the way post-scarcity is presented as more or less natural outcome of strong AI and space-opera-level physics, a post-scarcity society is entirely unthreatening to a modern-day billionaire (aside, I guess, from the decline in their relative condition - but in absolute terms, even Bezos and Musk would benefit enormously from being transported to the Culture, as it stands). It's not like we're achieving some sort of utopia by redistributing the resources of people like them (I am not claiming that's a good idea).