I'm a C# guy at work too. I can't say I've touched much C++ outside of college also a while ago, but I've been studying functional programming for a while and really enjoying the new concepts it teaches. It can be a bit humbling at times though.

I got some good perspective with https://www.coursera.org/course/proglang and you could do worse than taking grossman's excellent course. It helps to have some structure and a schedule when starting imho.

I will admit at times I wish I had more chops (closer to the metal i.e. C or C++), but I think I was eventually just more interested in new ways to think about programming, and I'm not sure I'd get the same pleasure out of digging back into C++.

Obviously, if you know something more about your intended use case (i.e. you want to program games), you can make a more informed decision.