It'll be interesting how he keeps the ESB revelation a surprise. I get the feeling it would be very hard to do but then again, we haven't seen what's coming yet. I get the feeling it would be VERY easy to preserve the ROTJ sibling surprise, though. It all depends on how it's executed on-screen.
Meanwhile, I'm avoiding spoilers on ROTS in hopes of giving myself some actual enjoyment while sitting in the theatre. There will be enough time to critique it after the third viewing.