I think the account switching in gmail is the single most annoying issue I've come across in lollipop. Most of the other changes are a matter of taste, the account switching in gmail is just plain bad. I have 5 accounts and can't even see all the "icon" versions at the same time... make the dropdown more distinctive and nuke the icons imho. I feel much the same about the icons in the message list too.

I wouldn't mind if the desktop/web interface were a bit more like the tablet sized gmail though... also if gmail proper could also see my other email accounts this way since there's no proper mail client in chromeos.