I'd say this seems to be covering way too much for a "short" movie. Just counting left-hanging plot-threads from other movies and you've got Loki's usurping the throne, the Infinity Stones and Thor's vision from AOU. Then add the titular Ragnarok (which, if looks remotely similar to the myth or even the comic book stories is a pretty epic event in itself with a lot of players from Asgard and other realms).
And that's assuming other potential players (like Jane, Selvig or Thanos) do not appear, at least directly.
So yeah, I'm not going to say I want a long movie for the sake of it being long, but this looks in terms of characters, scale and importance (it's the Twillight of the Gods after all or, at least, that's what they're selling us) even bigger than what The Dark World attempted to be (and I say attempted because that movie was butchered in the editing room).