CLI access perhaps, though there is a third party solution out there for that too. I just use chrome, which now works offline, can drag and drop into it, though not out of it, but it works well enough that I've never tried to install the sync client.

Nothing if you are using odeke-em's client. In my experience it's more useful than Google's desktop sync client.

Drag and drop file sync is nice. Google is much more generous with free space than Dropbox is (15GB vs 2GB), so I would use them more if they had a desktop linux client.