'Thor: Ragnarok' flexes its comedy muscles

Marking an ambitious detour into comedy, "Thor: Ragnarok" conjures sparks but doesn't quite catch lightning in a bottle. Sporadically fun and visually impressive, this third film works a bit too hard at flexing its laugh muscles, while bogging down in a midsection built around the enticing prospect of Thor versus the Hulk.

Part of the problem, frankly, is that Marvel has done perhaps too good a job marketing the movie, to the extent most of the best lines and moments (like Thor seeing the Hulk and enthusiastically shouting, "He's a friend from work!") have played repeatedly in the trailer. Even Led Zeppelin's "Immigrant Song" makes a slightly incongruous appearance.

To its credit, the movie makes the most out of an inordinately strong ensemble, surrounding Chris Hemsworth with reliable scene-stealer Tom Hiddleston as his brother Loki, Cate Blanchett as the villainous Hela and Tessa Thompson as Valkyrie, a fearsome warrior. Throw in a cameo by Benedict Cumberbatch as Dr. Strange and a meatier role for Idris Elba as the stoic sentry Heimdall, and there's a lot of power on screen even before the CGI pyrotechnics kick in.

It all starts promisingly enough, with Thor -- after what amounts to a James Bond-like pre-title sequence -- returning home to Asgard, where a newly freed Hela, the Goddess of Death, is on her way to lay siege.

Failing to stop her, Thor is inadvertently cast onto a dystopian planet Sakaar, presided over by Grandmaster (Jeff Goldblum, in fully manic mode), who forces his prisoners to engage in gladiatorial combat. Determined to win his freedom and face Hela, Thor is pleasantly surprised to discover that the Hulk (Mark Ruffalo) has landed there as well -- at least, until the first punch lands.

Marvel has handed the keys to the kingdom to New Zealand director Taika Waititi, who with his trio of writers unearths plenty of amusing character riffs, capitalizing especially on Thor and Loki's squabbling fraternal ties.

Still, there's a serious threat that must be addressed, eventually, as Thor spends ample time seeking to extricate himself from bondage and assemble the support he'll need to have a shot at defeating Hela.

"Ragnarok" (the title refers to the prophesied destruction of Asgard) is definitely a step up in class from earlier sequel "The Dark World." For better and worse, even these individual adventures have now been sucked into the maelstrom of the Marvel Cinematic Universe, where promiscuous cross-pollination among heroes has become the norm.

Bulked up for the occasion, Hemsworth remains an enormously appealing lead, capable of pulling off funny lines and slapstick silliness while still inducing swoons when his shirt comes off. He is, in many respects, the most special effect "Thor" has to offer, setting aside the inevitable free-for-all that, it should be noted, inflicts a higher quotient of carnage than parents tempted to bring younger kids might deem appropriate.

In a sense, a movie like "Thor: Ragnarok" represents the apex of Marvel's strategy -- a giant spectacle that in many respects plays like a comic book come to life, while being liberated enough to experiment with light-hearted quirks and idiosyncrasies.

At a fundamental level, Marvel jams enough high-spirited entertainment into the movie to ensure that it's worthy of the price of admission. It's just that armed with such a potent and promising arsenal, "Thor: Ragnarok" manages to feel less mighty than the sum of its parts.

"Thor: Ragnarok" opens Nov. 3 in the U.S. It's rated PG-13.