Personally it's the bundles and pinning. The bundles just worked more consistently than Gmail's tabs and made it feels fast (and safe!) to quickly archive a bunch of promo emails you weren't currently interested in.

Stars can be made to work like pinned e-mails, sort of, but it not consistent across the mobile app and the website and the UX just feels unresponsive in comparison. Pinned emails were much better separated than starred emails are today.

I think a bonus aspect was just design. Inbox didn't have to support as much legacy as Gmail and its design ended up being really sleek. Inbox overall just felt faster than using Gmail.

Trip bundles, pinning, mail previews. Inbox was much cleaner than Gmail. Gmail also feels slower than Inbox - spinners on startup.

And other UX issues: seeing previews of images right in the email list, font/UI makes it harder to find things vs Inbox. Inbox was a much nicer UI/UX.

Ads are annoying but I would have been fine with ads if it was integrated in Inbox.

And look, I understand that it doesn’t make sense to invest in/maintain two heavily used email clients. But the most infuriating thing is the trip bundles. That was my most used feature and such a distinguishing aspect of Inbox that it’s almost insulting that Google would tell me I can “find my favorite features in Gmail” when it’s blatantly not there.

I would pay to still use Inbox.

Apart from what’s already been mentioned (bundles, general UI, speed etc), the killer feature for me was how Reminders were integrated into the email itself. When an email came in that I couldn’t quickly resolve and move on, I’d write the short ToDo to myself about what I specifically need to do.

Back in Gmail I go to my flagged/starred emails and I know I’m supposed to do something about the email, but many times I’ve forgotten what what specific action was, so I open up the email, read through it and realize that I for some reason or other won’t take the action right now. Having to ”rediscover” actions in emails is such a waste of time. With Inbox there would be clear ToDos written, so I could easily scan a list of emails and pick the right one to take action on.

Also very useful with emails containing many actions within, but only one or a few are left unresolved, or an email with useful links for future reading, so easy to specify what in the email I should focus on and thus ignore the rest.

RIP Inbox. Miss you dearly.

For me, it was the way purchases and travel info were displayed.

Right before the shutdown I've booked a fight and hotel for a conference in June and it was showing as a big card in inbox. After the gmail switch there is nothing displayed, I have to go hunting for confirmation emails. So sad to see inbox go.

Besides bundles, the duplication of categories and labels hurts. Labels are second class (can't have a tab for instance) and categories are not user-generated. Lack of abstraction and orthogonality, a.k.a. "tacked on"

Not OP. My only issue with the Gmail app is the ads that sneak in.

Using Spark for Android and it seems to be scratching the itch so far

I miss snoozing emails right from notifications on Android a lot. With Gmail I need to open the app to snooze more than two hours.

Inbox: drag&drop a screenshot, then make it an attachment. Gmail: save it as an image in a folder, then select the attachments and browse to the file.

I miss the inbox UX & UI in particular.

Gmail seems slow and cluttered by comparison.