Re: "If you haven't already read the Wasp Factory. You wont regret it."
I think it's probably more accurate to say:
"If you haven't already, read the Wasp Factory. You won't forget it."
I loved it as a teenager and thought it was brilliant; but haven't read it for a while. I may not be able to tolerate the lunatic, over-the-top melodrama any more. I should have another go.
For his SF, _Use of Weapons_, _Consider Phlebas_ and _Look to Windward_ are among his best, I think. (_Look to Windward_ is one of the most upbeat books about nihilism I know.) (Incidentally, while his SF can mostly be read in any order, _Consider Phlebas_ and _Look to Windward_ need to be read in that order for maximum effect --- they're both standalone but are thematically linked.) _Feersum Enjinn_ is also great, and _Against a Dark Background_ is majestically bleak.
For his non-SF, _The Crow Road_ is a masterpiece. _Whit_ is huge fun and less lightweight than it first appears. Plus of course _Espedair Street_; and _The Steep Approach to Garbadale_.
Then there's his crossover books, which are largely unclassifiable. _The Business_, which I love. _Walking on Glass_ which is utterly bizarre. _The Bridge_ which does everything _Lanark_ tried to but so much better. And I haven't read _Transitions_ yet...