I absolutely love the fact that you can control the density of the emails. This was a huge deal-breaker for me with the new theme and made me go back to the old theme. I'd be more than happy to try this new look out.
Me too. I understand that the new design is visually more appealing and creates a better mood and sense of elegance for the user, but Gmail was designed for large volume email users, and it continues to be the best client for that use case, beating out every native app (at least that I've ever tried). For this type of user, packing more information on the screen is a huge usability boost. That might mean that Andy Rutledge will declare it crap and make a redux version that doesn't jab his monkey brain with a sharp stick, but it certainly doesn't mean that proportion and whitespace can't be used effectively on a more compact level.