Funny, but even though I've been reading science fiction my whole life I've never really been able to get into either of those series. I remember reading the original "Ender's Game" when it was a novella in Analog magazine, I believe. It did nothing for me.
I know when I was younger, and poorer I suppose, I could read some books more than once and still enjoy them. LOTR was one of those. I probably read it at least four times when in my 20's. But now I find I'd much rather find something new than go back to something I've read before.