I'm assuming it's not available for everyone yet.
The great thing about Inbox is that it allows you to sort your mail based on importance. And by importance, I don't mean just by labeling an email important.
Inbox lets you add a reminder to your emails and have the emails reappear in your inbox at the time you will be ready to deal with it. It lets you deal with important tasks first (tasks, not emails) and you can either snooze or set reminders on the rest for a later date. Once you're done with the task you can simply archive the email by selecting "done".
Inbox allows you to handle emails as a to-do list. Which is great because I am sure most emails are just that. Something you have to deal with when you have the time.
What I don't quite like about this system is the way it handles labels and incoming messages. On my mobile app, I no longer know which account has the new email. A notification will be apparent on the app icon but once you've opened the app, you can't tell which account that notification is for without checking everything.
Next, I label all my emails because it's just easier to browse through them when I'm looking for information or things I need to do. I do not enjoy having to double check if every email is labelled. This is important to me because I have people coming to me asking about when certain emails were sent or received or if certain documents have been sent out.
If these two issues can be fixed I'll be very happy with the new changes (that may replace gmail).