I tried Inbox, but wasn't impressed. It strips so much of gmail away that it is basically "Gmail for beginners". You want filters, labels, etc, then it is worthless.
Actually, Inbox is Gmail for power users, for people who have massive volumes of e-mail to manage. It takes a little bit of work to figure it out and set it up, but once you have, it's awesome. There are some features it lacks, like complex filters (simple filters are very easy to set up; you just move a message to a label and Inbox asks if you want to always do that. Click "yes" and you have a new filter rule), vacation auto-responder and the like, but you can always use the Gmail UI when you need to set stuff like that up.
The Inbox features that that make it great for heavy e-mail users are:
Many people use their e-mail inbox at least partially as a task list, especially their work e-mail. This results in having to keep e-mails that for you can't work on yet sitting in your inbox, cluttering it up and making it harder to process new e-mail. When you snooze an e-mail, it goes away until some point in the future. You can pick a date and time, or even a location (requires using the Inbox app on your mobile device). Heavy application of snooze with well-chosen times/locations lets you clear all of the stuff you can't do yet out of the way, knowing it will come back later when you can handle it.
Bundles are just Gmail labels, but with an additional setting that tells Inbox to group them in the inbox. This is fantastic for high-volume mailing lists. With Gmail you can get almost the same effect by setting a filter to apply a label and skip the inbox, but then you have to remember to actually go look at the label from time to time. With bundles, you get the same grouping effect but the bundles show up in your inbox so you don't forget to go look. The reason that grouping (by whichever mechanism) is useful is because when you have large volumes of email, most of which you don't actually need to read, it's much faster to scan through a list of subject lines and evaluate what's important and what isn't when you already know the context.
My process for plowing through a busy mailing list is to scan the subject lines and click/tap the "pin" icon on the few that are interesting, then "sweep" the rest. A single click or gesture archives all unpinned items in a bundle. Then I handle (or snooze until I can handle) the pinned items.
I also have a bundle (label) called "Me" that is applied by a filter that looks for my name or username in the To line or the body of the message. This helps me to be sure that I notice e-mails where people are mentioning me or asking me questions. It's the first bundle I look for every time I check my e-mail. Similarly, I have a bundle that extracts e-mails that reference my project's name. That's the second bundle I look at. Other high priority bundles are e-mails from the code review system and e-mails from the bug tracker.
Obviously there are many e-mails that mention both my project and me. That's fine; bundles are labels not folders, and it's perfectly reasonable for an e-mail to be in more than one of them. When I archive a message in one bundle, it disappears from the others. So, often I'll look at Inbox and see the "Me", project, code review and bug tracker bundles displayed, but by the time I've processed everything in the "Me" bundle, the other three have disappeared.
I think this vies with snooze as the killer feature of Inbox. By default, a bundle appears in the inbox whenever you receive new mail with that label. But there's lots of stuff, at least in my inbox, that I don't need to see immediately. Having low-priority stuff displayed instantly distracts me from my work, or obscures truly urgent e-mail. Also, it's more efficient to handle low-priority e-mail in bulk. So, you can specify that a bundle should only appear once per day, or once per week. Inbox will accumulate e-mail in delayed bundles and only show the bundle at the specified time.
When I start work in the morning I have a dozen or so bundles containing low-priority e-mail. I can quickly scan each of them, pinning the items I care about and sweeping the rest. I have a few bundles for purely informational mailing lists which are set to display once per week, so I only see them on Monday morning.
I'd like a little more granularity on this feature. Specifically, I'd really like to be able to set some bundles to show, say, every three hours. Then I'd only allow the highest-priority bundles to show immediately, giving me larger blocks of uninterrupted time but with the knowledge that I'll still get notified of truly urgent stuff immediately.
It took me a while to realize just how valuable this is, but it's really great that the mobile and web UIs for Inbox are virtually identical. I don't have to have two different flows for handling e-mail on mobile vs desktop. The mobile UI is a tiny bit better because of the gestures a touchscreen interface can provide, but my process for using it is the same.
One common complaint about Inbox vs Gmail is that Gmail's more compact; you can fit a lot more stuff on the screen with the Gmail UI. I find that isn't a problem, because the Inbox workflow mostly eliminates the need to scan through a big list of messages visually, looking for something in particular. The need to do that arises mostly (for me, anyway) when I'm keeping a lot of stuff hanging around in my inbox. With Inbox, I don't do that. I snooze it or I archive it, so my inbox is empty nearly all the time. If I need to find something that I've snoozed or archived, I search for it.
Bottom line: If you're a heavy user of Gmail, you should really take a good look at Inbox. Odds are you'll never go back.