You know, if, at 18, I had needed to choose a favorite author, it would have been RAH, hands down. I think it's fair to say that I've read everything he's written except for his first novel (that was only published a couple of years ago).
So, a couple of months ago I was browsing my shelves and picked up Stranger In A Strange Land for the first time in probably a decade and a half.
Boy, it annoyed the crap out of me.
Now it's funny, because I mentioned this on a mailing list I'm on, and someone who knew me in college mentioned that he found that interesting, since I had once said it was an incredibly important book that had changed my life.
The thing is, though, it did. And all the things in it that caused me to change are still there. But I couldn't get over all the things about it that annoyed me so–the awe-inspiring condescension of the main characters towards everyone else, the spectacularly patronizing attitude towards women, oh, it drove me crazy. But you can draw a very straight line between what I believe now and what that book exposed me to.
Just the other day I picked up The Number of the Beast which I haven't read in at least as long as Stranger, and found it absolutely unreadable. I skimmed it, but basically had to hold my nose to read any of it. And yet I remember liking it immensely.
There are others that I've read more recently than that that didn't offend me. Basically, the simple adventure stories still work for me; there are things that occasionally annoy, but in the main they're no worse than a lot of pre-new-wave SF. But most of his later novels-+his largely "high-concept" output post+/Stranger/–I now find mostly unreadable, because of the absurd didacticism.
Except, and this surprises no one as much as me, The Moon Is A Harsh Mistress and Starship Troopers. Yep, Heinlein's famously "militaristic" novel, and his novel of libertarian revolution–two things that, in general I have no time for.
I guess it's like family. They may annoy the hell out of you, but you're still related.