I loved “Trainspotting”. It often gets disturbing and dark, but Welsh doesn’t do that in a pointless way just to increase the shock factor. It feels more like he’s showing us unprocessed snapshots of Scotland’s “lumpenproletariat”, like a photographer going around the seedy areas of Edinburgh, without trying to judge or explain anything; just a story that leaves out any sentimental or intellectual b.s. but still makes you think things like “How did it end up like this? Is there a way out?”. Probably that’s why the film adaptation worked so well — the book is “showing” rather than “telling”.
Tackling social issues like addiction, violence, racism, politics, always carries the risk of sounding like a know-it-all snob. I think Welsh has managed to avoid that, he took the talk down to the street level, successfully demonstrating that these things concern real, breathing (and often likable) people and not just abstract stereotypes.
I read a translated version; the original might be a bit more difficult to read due to all the parts in Scots, but it would probably feel more authentic and colorful for the same reason.