I've read the first two Commonwealth ones (actually just finished a rare re-read). The first one of the void trilogy is sitting on my shelf, but I got some other stuff to get throught first.
I read the Nights Dawn books as a teenager. They were great then.
Hamilton is certianly up there with Banks in terms of ideas. All his characters tend to gel into a few archtypes (grizzled vet, nerdy type, perfect intellegent untouchable female, randy intellegent very touchable female etc.), but his prose and dialogue generally get me through. I think Fallen Dragon is probably his best, and a nice, rare example of good standalone sc-fi with big ideas and a character driven plot co-existing.