Caught this today.
It's definitely good. Had a lot of fun with the film. But it certainly doesn't have the imaginative disorder of the first film. Where the first film feels like a painter throwing whatever surreal idea and bit of paint he has at the canvas in a euphoric frenzy of artistic verve, this film feels much more structured and deliberately paced. But as somebody said previously, it more naturally mirrors where these characters are now at, as opposed to their previously drug-induced rabidness.
It does lean heavily on the original, but more to naturally inform the present story and connection/dissolution between the characters. It's necessary as opposed to lazy nostalgia-mining.
It's not up there with Boyle's cream of the crop, but it holds its own place a good deal above the likes of Trance.