I've only used Inbox since the very first day it was released, and I loved it; it's a simple mix of concepts that resulted in an experience that has made mail much more pleasant (and less of a hassle) to me. I don't think anyone that has intensively used Inbox in the last years may think even remotely that the new Gmail is a similar experience, because it definitely still has a completely different look and feel.

I think I'll switch back to Thunderbird on desktop for the time being, given that the hassle (and delays) of having several POP3 accounts configured on the Gmail website isn't really worth the effort without Inbox.