For Python, there is a choice of the jedi library or the rope library to do refactoring and smart completion. This in addition to ctags and the like. I imagine other languages have similar things.
Smart completion is fine to me, but the refactoring is a potential problems. It seems there isn't an open source refactoring tools as good as PyCharm for python.
This one doesn't need gVim, with rgb() and rgba() support https://github.com/ap/vim-css-color