Consider Phlebas, (admittedly his first) - but thankfully The Hydrogen Sonata was much more the kind of on-form writing I've come to enjoy.
I will get one moan out of the way up front - it's too long. I can't be doing with these doorstop books as a whole, and quite a lot of it felt in need of a good tightening edit. But having said that, there's a whole lot to enjoy here in the complex machinations between different races and seeing different Culture ships exhibit behaviour that isn't necessarily quite what you'd expect.
As usual with Banks there's plenty to ponder in the 'what if' department, here particularly around the concept of 'subliming' where individuals or whole races opt to become part of a disembodied multidimensional spacetime - probably some people's idea of heaven and others of hell. But equally, as Banks did so well, there's plenty of straightforward action, humour and adventure.
This is definitely one of the Culture books I'd recommend to get immersed in the Banks' canon - as all his best books do, it sucks you in early. There are a lot of characters to get your head around, and occasionally I struggled with which ship was which - but generally speaking, as long as you're prepared to go with the flow, it's a great ride.