Cause movies have at least 90 minutes of footage to work with
I think HotS will take you more than 90 minutes to finish! :P The story is driven by X minutes of cinematics and X hours of gameplay/narrative. Far more than any movie I've seen!
As for your story hopes, read on if you don't mind spoilers:
From what I could ascertain, there aren't really any heavy twists in the story. It's a brute force mission of revenge whereby Kerrigan (with Raynor standing by her side) finally gets to kill Mengsk. The end. They must have done a great job of hiding any possible link to Legacy of the Void, because I didn't find any.
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