It turns out Warframe's gameplay gains absolutely nothing of value from being set in an open world. There's no reason to explore, nothing interesting to find, and the only meaningful difference between bounties and regular missions is how inconvenient they are (and the massive amount of bugs really exacerbates this). So far I've seen literally nothing to suggest that this entire update wasn't a complete waste of effort.
Edit: Well, other than the attention it has drawn simply by existing, but we'll see if that lasts.
Gains nothing of value from being in am open world? I can't disagree more. Warframe's hyper fast and fluid movement system can finally be let loose in a massive playground. It feels great to bullet jump and aim glide down a mountain. And snipers, for the first time, are actually a lot of fun to use. It also allows for big, map-spanning fights with eidolons, who would otherwise be too boxed in by typical Warframe maps.
There are all manner of resources to find out there, and some of them are only located in certain regions. I also think there is lore hidden in the caves, but I need to confirm this.
Just for comparison, what would you say was a good update to Warframe?