More of a Meta experience than an actual sequel.
The scam is replicated, Spud turns out to be the writer of 'Trainspotting.' Begbie comes back as a level boss not a character. McGregor plays himself "You are looking well, Mark. - Yeah, every one says that." - sh!teating 'I'm Obi-Wan you know' grin. until he starts doing crimes and you remember he is playing a character. The soundtrack is just a collage of the original. Kelly MacDonald's cameo. The mountain. The flashbacks. The car bonnet.
It seem like they gutted the Porno elements to cram in as much Trainspotting as possible. It is all too self referential, like a fractal version, a remix, not a sequel.