(M) ***

Director: Alan Taylor.

Cast: Chris Hemsworth, Natalie Portman, Tom Hiddleston, Christopher Eccleston, Anthony Hopkins, Stellan Skarsgård.

WITH its sequel to Thor, the eighth movie in "Marvel's Cinematic Universe", the comic book company's film arm is proving to be not unlike Thor himself - pretty much bomb-proof and unstoppable.

Even Iron Man 2, the runt of the MCU litter, made a mint, but if you're looking at Thor 2 and expecting a turkey or a flop, keep looking.

It's far from perfect - The Dark World has got some serious script issues - but even these can't detract from the fun and spectacle on display.

But be warned - the MCU is becoming an increasingly tangled web of stories and newcomers are less welcome with each new film. References to past events from the series fly by faster than Thor's hammer so prior reading is expected. If you haven't seen the first Thor or even The Avengers, this sequel is not the place to dive into these tales of superheroes, gods, and their growing mythology.

The big baddies this time around are The Dark Elves, a scary bunch of hi-tech ancient ones led by the dead-eyed Malekith (Eccleston), who looks like a pointy-eared shark with a ponytail.

He's seeking vengeance for a past defeat, which he hopes to pull off with a universe-destroying MacGuffin known as the Aether. Naturally, Thor and his hammer are out to stop him.

There are some surprising plot holes in the early stage of the film that don't feel like mistakes, but more like the film has been slightly trimmed to cut down the running time, leaving the audience to fill in some mildly annoying gaps along the way.

Despite this - or maybe as a result of this - the plot moves along at a good pace, dotted with impressive fight sequences, good gags, and a few jaw-dropping CG sequences.

Amid the carnage are good characters and some great performances. Hemsworth seems more at home than ever as Thor, more confident than cocky this time around, while Hiddleston's Loki is again a highlight. Their relationship is central, as it was in the previous Thor film, but has evolved into something new and intriguing this time around.

It's these returning characters - and the development and relationships given to them by the writers and actors - that are a highlight of the film, bringing depth amid the bombast and explosions. The connections between Loki and Thor, Loki and his parents Frigga (Rene Russo) and Odin (Hopkins), Odin and Thor, Thor and love interest Jane (Portman) make this a healthy melodrama somewhere between Shakespeare and soap opera. The return of Skarsgård's Erik Selvig is also hilariously welcome.

The humour really is a highlight - it could be argued this is the funniest Marvel movie to date, even outpacing the typically Whedon repartee of The Avengers. Some bit players are there only for gags, such as Kat Dennings' Darcy, Chris O'Dowd's Richard and the otherwise unneccessary Ian the intern, but it is Loki who is again a scene-stealer, delivering moodbreakers and withering putdowns with humourous ease.

The humour does ride on a knife-edge though. It's a necessary foil to the po-faced business of Norse gods flying between realms and saving the universe, but it almost goes too far into self-ridicule (and some fans might find the hilarity hard to stomach).

Take for instance the ending, which is great - it's wildly inventive and hilarious. But it teeters on the edge of wackiness, balancing precariously over a chasm of plot-holes that are filled in with technobabble so as to be less obvious. If you can laugh along and still be gripped, it's a spectacular finale.

Thor was seen as being a risk for Marvel first time round, but they pulled it off with casual ease.

It seems to be a trickier world to manage on a second outing, but fans will be pleased.