No, it won't replace FB entirely. I've been using for a while now and really like it much better but know I won't be able to convert all of my peeps. So, I will have to use both.
What I do LOVE is the ability to view just 1 circle if I want, or to post to just certain circles. Cuts down on all the 'clutter'. That's what I dislike about FB so much, games/likes/general clutter that you can't avoid. G+ makes it so easy to filter who you are posting to, or what group you want to read.