If you’re of a certain age, Danny Boyle’s 1996 film “Trainspotting” was an earth-shattering, mind-expanding event. There was a Before “Trainspotting” and an After “Trainspotting,” which was accompanied by a sudden affinity for ambient electronica, Scottish accents and buzz cuts. There has never been anything more heroin chic than “Trainspotting,” and in capturing the world of Irvine Welsh’s novel, Boyle made something fresh, new and edgy that wasn’t just of the zeitgeist — it defined the zeitgeist.

The angry, existential “Choose Life” speech delivered by Ewan McGregor’s Renton perfectly captured the angst of ‘90s modernity, and 20 years later, there has never been a moment more ripe for another one. Perhaps that’s why Boyle and the gang got back together to revisit the old Edinburgh haunts in “T2 Trainspotting.”

They may be grayer, but the gang remains remarkably the same. Renton returns back to his hometown after a health scare (in the gym of all places, yuppie scum) to find Sick Boy (Jonny Lee Miller), Spud (Ewen Bremner) and Begbie (Robert Carlyle) much the same as when he left — which was when he cheated his pals out of several thousand pounds while making off with the score from a heroin deal.

John Hodge, who was Oscar-nominated for the “Trainspotting” screenplay, is back to adapt Welsh’s characters to the screen in “T2.” Borrowing some plot details from the follow-up novel, “Porno,” the story follows Renton’s return and attempt to mend fences with his old friend Sick Boy, which involves trying to open up a brothel with the help of his Bulgarian sex worker girlfriend, Veronika (Anjela Nedyalkova). Begbie, in prison, is raring to get back to the world, while Spud is fed up with junkie life.

The screenplay concerns itself with the nature of memory and nostalgia, begging the question that we’re all asking, 20 years after the first film: Why revisit? Why now? This referential treatment is wise — it’s truly the only way a sequel like this could get away with existing, by interrogating its reason for being. But it’s also its downfall; that interrogation becomes a quicksand in which the film is repeatedly and unfortunately bogged down.

Boyle’s signature kinetic cinematic style brings energy and life to the material, reminding audiences of the audacious jolt that was “Trainspotting” in 1996. Bright, poppy colors, Dutch angles galore, off-kilter framing, rapid camera movements, mirror reflections and hallucinatory streaks of light create an intoxicating visual energy that’s easy to get swept up in. All of the effort in the craft is palpable, nearly desperate, but to what end? It feels like trying to re-inject life into a corpse overdosed on nostalgia.

As shared histories (between the characters within the film and between the film and the audience) come flooding back, “T2” can’t escape its own memorializing. While “Trainspotting” introduced audiences to a starkly new world — new sound, new accent, new look, new city — in retracing this path, there’s no new ground for “T2” to tread. The only real pleasures are in fleeting moments of recognition and enjoying a chuckle with old pals. After awhile, all that reminiscing becomes dull. Why relive “Trainspotting” through the fractured lens of “T2” when you could just relive the magic and re-watch “Trainspotting”?