@elextr yeah we don't have something too intelligent for completion, as @techee said it's somewhat more "autocorrect" with enhanced capabilities. But like him, I still like it :)
If you want true awesome completion, I'm afraid there's only one direction to go: make the completion pluggable in a way that allows plugins to provide their own completion as they wish, their own symbol tree, etc, so it's easy to implement plugins using things like libclang and others. It has annoying downsides like the need to setup a complete "project" with build options and all -- goodbye "build system is enough". But that means specific work for *each* language, with virtually nothing that could be shared. I guess such an API needs to allow plugins to show the autocomplete and calltip boxes, fill them, and provide TMTags. Maybe other things.
Still, as @techee said, if we get a nicely groomed pig, "all" we need need are good parsers (which we work on, and everyone at *ctags does, too, which profits many apparently), and that gives something still very nice to many people and more exotic languages for which nobody will have written a full plugin with true language insight.