This movie shouldn’t exist. It shouldn’t work. It’s great.
There’s a type of movie that internet film nerds refer to as a “legacyquel”. This term applies to a sequel that is released many years after the original, in which the original actors play their original roles. When this idea fails, like the recent Independence Day movie, which brought back a dead character with a flimsy explanation, it can fail spectacularly, but when it succeeds, like Star Wars: The Force Awakens does, we can celebrate the return of our favorite characters in an entirely new story line. T2: Trainspotting is one of the latter instances.