When it launched I had several friends on g+ that were not on Facebook. Facebook already had a bad rep, but Google was still cool. The circles were a great idea. I didn't see any problems with the ui either.
But there was simply not much to do, contrary to what you'd expect with all the other Google services available.
“Friends on G+ that weren’t on Facebook” <== this was an opportunity
I was still very high on Facebook kool aid at that time. It may have had a bad rep to some people, but this sentiment was years away from reaching people like me.
Note that I am about as much of a Facebook insider as possible without actually having worked there. I personally know most of their top execs, Zuck interviewed me in 2007, turned down a PM offer to join Bebo but stayed close with a number of them for years. I would have loved to be filthy rich with those options, but if I had joined I would feel guilty for the destruction I contributed to.
But there was simply not much to do, contrary to what you'd expect with all the other Google services available.