Sorry to be that guy, but it would be great if that left hand nav would auto collapse into a hamburger button on mobile. It's taking up sooooo much space, and it shrinks the content to the point where it's unreadable.
You bring up a good point, IMO: the "Open in Data Viewer" button is far-too obfuscated. If I hadn't used Enigma before, and hadn't already known what was contained in a previously-visited dataset, I too would have assumed that I hit a dead end because the button was the last thing I noticed on the page.
The horizontally-flowing layout is problematic overall, but placing that "Explore Data" button much higher in the right-most column would be a decent compromise:
http://imgur.com/a/lS7ks
