My quick thoughts on the iPhone app:
Good overall. It's just as good as most of the new line of productivity focused apps that have been released (and acquired) over the last year.
My quick thoughts on the web interface (inbox.google.com):
This is where it's really shining for me. Finally email doesn't feel like a spreadsheet with buttons anymore. It feels like Gmail should feel in 2014. Now that I've started using this, it would feel painful to go back to normal Gmail. You just kind of have to start using it to understand, but I really like it.
All of the new features (reminders, pinning emails, bundles, and one-button archiving of bundles like promotions and forums) are great . I've used almost every new feature already and they all feel like a natural part of a flow.
The only nitpick I have at the moment is the integrated chat in the web interface. It's defaulted to the Hangouts style chat, which I'm not a huge fan of. In old Gmail you have a choice of using the normal version of chat or Hangouts chat, and I've always turned off Hangouts chat. I really wish you could do that here, but I'm not seeing an option for it and my guess is there will never be one.
Overall however I'm really happy with this new version of Gmail and will continue to use it everyday.