The first view is pretty self-explanatory.
It's called the deep-dive because you're lending your attention to whoever's page you're looking at for all
nine images of their first gallery, one picture at a time.
On the one hand, the deep-dive is pretty immersive. It is the only view without any preview images of what's to come, so you're letting yourself be immersed in the full experience of the person's whole first gallery, one picture at a time.
On the other hand, you don't see anything of the other eight galleries they have, so you're only really taking a peak at what this person has to say, without getting sucked in and spending a whole hour clicking around their page.
Since the deep-dive is the default view, and probably the most common view since it shows the fewest pictures and sucks you in the least, the first gallery is the most important gallery. If you had someone's attention for just nine pictures, what would you have to say?