I am a messaging professional, so my work is based around designing email systems. When I used Inbox for the first time I was delighted.
The main issue with typical mail clients is that they are not very intelligent. You have to do all the work by yourself, but even then it is very difficult to make email work for you, and not the other way around.
You can organize your mail in folders, subfolders, archive it, and create many rules that handle all incoming communication.
With Inbox I do not have to worry about all of that. Inbox will show me important mails and will notify me. Unimportant mails (like newsletters) will not cause a notification trigger. I can choose to read them when I have the time and I will not get bothered by Inbox. My purchases will automatically get grouped together. This is a very nice feature. Before Inbox I had a special folder and associated rules for handling my purchases. Every time I purchased something online from a new company, I had to go and create a new rule, or update my existing rule. Now, I let Inbox handle that for me.
Inbox is really impressive in organizing my email. (and I get a lot of email).
Inbox makes Email work for me. It shows how important Email is.
The only reason I am using my gmail account for mail is Inbox.