On the downside, utilities like tagging, blame and stash do not seem to exist. The account linking system from the old GitHub client hasn't changed and you can't clone from anywhere that isn't GitHub. Revision history is a bit ~too~ simplified and you can't really see at a glance what branches are deriving from where, and you can only see the history of one branch at a time.
I'm sure newbie developers on Github might appreciate the simplified UX/UI, but it's missing a ton of features that are useful in an environment with multiple devs.
This feature drove me nuts with their old client. One day they're going to realize that it throws away a very useful Git feature.
A few years ago we tried setting up marketing's content creators on the Mac GitHub client. After that, far too many conversations went like this:
"Try pulling the new changes."
"Right, sorry, forgot. Hit sync to pull down the new changes."
"But won't that push my mods?"
"I suppose... I don't know."
"I don't want to push my stuff yet."
"OK, dammit. Open a terminal..."