>>5,6
Plan 9 is like Unix but more Unixey than Unix. It's like Unix². Understandable from the people who created Unix. If you dislike Unix, you'll probably hate Plan 9.
Plan 9 is not Unix. If you think of it as Unix, you may become frustrated when something doesn't exist or when it works differently than you expected. If you think of it as Plan 9, however, you'll find that most of it works very smoothly, and that there are some truly neat ideas that make things much cleaner than you have seen before.