> The first part left me quite underwhelmed

The books are chock full of the various character's internal dialog, and when you make the choice to leave that aspect out, there is quite a bit of richness missing.

This version went the "show, don't tell" route. Visually, its amazing, but so much additional information from the book to help you understand the characters, the groups they belong to, and their motivations was left out.

I think the Sci Fi channel Dune miniseries did the best job of putting across the full richness of the book, albeit with a made for TV budget.