Well, I finally got a chance to see this! So, where to begin?

Rating: 8/10 (15 November 2017)

Surtur's dungeon, I guess.
With no montage to back it up, Thor tells this long-dead skeleton how he wound up in chains inside a glorified bird cage. And the back- story is a little vague; referencing a search for something called the "Infinity Stones."
Hearing this, I thought to myself: "Say what?! What installment did I miss in this franchise?"
But, I quickly forgot that in all my excitement over the opening battle! Which, by the way, was fought to the tune of Led Zeppelin's famous Wagnerian pastiche ("ah-ah-ahhhhhh!" and all). But, then came the first of several surprises.
Heimdall; replaced as Bifrost gatekeeper by a low-rent Viking named Skurge?
Loki; posing as a suddenly--and uncharacteristically--hedonistic Odin?
And the real Odin: somehow rendered amnesiac and then marooned on Earth (perhaps as an adviser to stranded Autobots)?
What the heck is going on, here?????
It turns out to be a Machiavellian ploy by Odin to deal with the coming of Hela, "goddess of death." In this film, she is not depicted as Loki's daughter (and, therefore, Thor's niece) as she is in classical Norse mythology. Rather, she is Thor's long-lost older sister!
And, boy, is she p****d off.
Killing Thor's three favorite warrior companions (blond Fandral, redheaded Voltstagg, and Lapp/Sami-like Hogun the Grim) with almost laughably easy speed, she makes Skurge her personal executioner. A deal he soon regrets accepting!
Thor's ultimate show-down with them (including a reprise of Led Zeppelin) is capped off by a desperate gamble that's equal parts Trojan Horse and "Hail, Mary" play. The ploy succeeds, of course. But, at a terrible price.
And, no; it's not the death of Jane Foster! Apparently, she's already dumped the "god of thunder" before the movie even begins. No in- story reason given. The real-life reason was probably casting unavailability on Natalie Portman's part. In any case, I deducted one star for her absence.
I deducted another star for turning the Grandmaster from a blue- skinned, nearly omnipotent Elder of the Universe...into an anorexic-looking version of that Roman fop from GLADIATOR. The one who tried kissing Joaquin Phoenix's butt with that "Battle of Carthage" fiasco?
In short; this is a pleasantly action-packed little time-killer on its own merits (as with the first two Thor films before it). But, with regard to being integral to the cinematic saga of the Avengers, as a whole? Not really. Not unless the opening scenes of their next flick serves as prequel to the opening scene of this one!