The sidebar looks atrocious and doesn't match Material Design. Animations are buggy and get stuck, so MD-like effects like the pulsing have leftover circle artifacts on objects. It looks worse with a custom theme/background. It's harder to read because of the new font, making a lot of the text look blurry and harder to read. The icons are too small and insignificant for me to get use out of them (and why do I still have to click a submenu to get to "Mark as Unread")?

And that was just my first 5 minutes with the app. Maybe some gripes are derived from the comfort of using the previous app, or even small bugs with the new release, but overall the experience hasn't felt like an improvement at all.

I tried it for 15 minutes and went back to the old design.

It feels fresh on a UI level, but in the end usability is what really matters for a tool. In general I think UX is worse now.

Text is harder to read with the new font. Also there is just too much white, everything is floating with no visual structure, no contrast. Icons are smaller. Animations aren't smooth in my top of the line 5K iMac. Etc.

This new Gmail doesn't have the quality and polish that we've come to expect from Google's web apps.