A Very Harold & Kumar 3D Christmas doesn't take very long to let us know its intentions: within the first five minutes, we have encountered a scene in which a heavily bearded and altogether worn-out Kumar Patel (Kal Penn) and a mall Santa Claus (Patton Oswalt, the first of many immaculately-placed cameos in the movie) are smoking holiday-themed marijuana, and exhaling directly into the camera, the fingers of smoke gently floating out over and into the audience in gloriously crass 3-D CGI. This is not the last time that marijuana smoke will be breathed at the viewer, nor the last time that dodgy special effects will be thrown out for our enjoyment, nor the last time that there will be an intensely forced and obvious 3-D effect pitched right through the screen in defiance of all good judgment and taste. Since anyone remotely likely to pay money to see A Very Harold & Kumar 3D Christmas is presumably looking for exactly these things, I feel the only honest thing to do is to declare the movie a success.

If you missed it, Harold Lee (John Cho) and Kumar were the stoner heroes of 2004's Harold & Kumar Go to White Castle, almost without question the finest pot comedy of the modern age, and its 2008 sequel, Harold & Kumar Escape from Guantanamo Bay, a much more rickety and conceptually uncertain attempt at satire that was good-natured enough that I, for one, still liked it fairly well. 3D Christmas strips out most of the unnecessary complexity of the first sequel and returns us to the basic plot structure of the original: Harold and Kumar are obliged to go back and forth and up and down and all about over the course of one terribly stressful evening on a Quest, and the consumption of drugs is involved.

This time around, it's six years after the events of the first two movies, and the boys are no longer on speaking terms, let alone the best buddies that they were before: Kumar is still a commitment-free pothead, having been dumped from medical school for drug use, while Harold has married Maria (Paula GarcΓ©s), and is trying to put together the perfect Christmas to impress her demanding father (Danny Trejo). A chain of contrivances that are only reasonable because this is the kind of film that it is throw Harold and Kumar back together with a burned-down Christmas tree on their hands and just a few hours to replace it before a very angry father-in-law returns to destroy Harold utterly. Along the way, there is the customary assortment of wacky problems: Kumar's feckless neighbor Adrian (Amir Blumenfeld) gets them involved with a Ukrainian mobster, Harold's co-worker and only friend Todd (Thomas Lennon) and his infant daughter have gotten tangled up in all the misadventures, Neil Patrick Harris and his very, very game husband David Burtka appear as "themselves" in a scene that finds a tidy way to dispose of NPH's well-publicised homosexuality while fulfilling the Harold & Kumar charter that he appears in every movie as a, shall we say, vigorously straight man.

It's all relentlessly lowbrow and in questionable taste, of course - this is a pot comedy. Even within the limits of that genre, I suppose that every viewer will have his or her own standards for whether a running gag about a baby ingesting a cornucopia of narcotics counts as "comedy" or just cruelty. And setting aside issues of taste such as that one, there's still a lot of places where the jokes swing and miss: the incredibly forced reference to Penn's stint with the Obama administration leads a not-insignificant pack of moments that fall to the floor with a horrible clang the moment they are sprung upon us; I'd add to that list virtually everything including the Wafflebot, a cutesy waffle-making droid that is meant to be the best-selling toy of the holiday season, and not apparently because it is appealing in any way whatsoever.

And yet the film works, basically: shockingly, it even manages to deepen in its fumbling way the series formula, by jumping forward six years (that is to say, by catching up where the chronology should be relative to the first movie) and seeing the protagonists have grown apart, as people do, and realising over the course of a series of misadventures that they're still basically the same guys they were way back when, and they still basically like each other, and it's a huge shame that they've drifted apart - as people also do. You kind of have to hunt for it in amongst all the deliberately stupid japing and 3-D gimcrackery, but there's a real sweet little movie in there about the durability (or not) of friendships as years go by and people's interests change, given legitimate heft and meaning by Penn and Cho's lived-in performances and considerable chemistry with one another.

Of course, the stupid japing is largely what we're here for, and while 3D Christmas was never going to match the playful inventiveness of White Castle, which successfully turned a case of the munchies into a Homeric journey, it's also less strained than Escape from Guantanamo Bay, and its uniformly classless jokes - everything from slow-motion three-dimensional gewgaws (though this tapers off as the movie winds on) to a penis-based riff on the "tongue stuck to a flagpole" scene from A Christmas Story - are presented with a genial "aw shucks" kind of shrug: director Todd Strauss-Schulson is no master of comic timing, but he never permits the humor to start taking itself too seriously, as in e.g. The Hangover, Part II, in which similarly trivial idiocies were presented like the word of God. The soul of any stoner comedy is that it's basically just a laid-back way to waste time with amusing, agreeable people, and this is something that 3D Christmas does terribly well: we get to hang out with people worth the hanging out, and chuckle amiably when they do silly things. It is, in this respect, the best possible Christmas movie/pot movie hybrid: low-key and friendly and goofy without ever being deliberately mean.