In mobile but not only. 1. In one page checkout (default nop) it's good to be showed where we make mistake or miss something (like name ot zip code). Now we click next and until don't start scrolling we don't see what is wrong.
2. Maybe it's possible to add second way to show reviews.
Now we have them in the tabs, but not all people click in this. Maybe below products/description it's worth to show last reviews. It's more friendly - maybe. ;)
3. I read this and thiss will be great, if you add possibility in product page to stick add button. I think only on single product page, but i read it's a sugested "best practice" in mobile design. But i see this also in desktop and when we have long page with long description it's can be a great solution.
4. I'm not sure but maybe is diferent solution to make tap/swipe poduct gallery. Now we have standard gallery option and the second one, where on mobile we have swipe mechanism, but on desktop really big pictures. When we have product with wvariants or 10-20 images page on desktop is really long... Maybe is a way to add on mobile swipe mechanism, and on desktop standard gallery... Or maybe it's possible to set it in admin/threme panel?