I don't think I read most of those until I'd already reached adulthood - I didn't go back to the classics until I was in my early 20s when I had more money, easier access to second-hand bookshops and had exhausted the SF collection I inherited when younger. My first introduction to the classics were Anne McCaffrey's Pern books and Niven's
Ringworld - actually, they were more or less my first introductions to adult SF and the early Pern books are SF/fantasy crossovers anyway. Basically, dragons in one and a big toy in the other were concepts I could understand (I was fairly young when introduced to them, maybe around 9 or 10).
Of the list, the three I remember reading before adulthood were the following (I
think 2001 was the first of them but I haven't a great deal of confidence in that):
Dune,
2001 (and subsequently
2010 and
2061) and
Stranger In A Strange Land. I can't really remember when I read them and what I thought of them (other than
Stranger being somewhat bland and that it should have finished a good 100 pages before it did - which was reinforced when I went back to it a few years ago and threw it into the charity shop box immediately after finishing it), but it would have been somewhere in the 13-15 age range. I remember coming across C J Cherryh's
Downbelow Station around this period as well and liking it more than any of those, although
Dune grew on me as I got older and reread it.
I admit I don't remember when I came across
Hyperion. I have a feeling it was in my late teens, as I do remember seeing it on the shelves for at least a couple of years before I bought a copy, and I didn't look at the sequels for several years afterwards.
Hitchhiker's Guide I was introduced to when some repeats of the television series were shown (I don't remember exactly when). I didn't go near the books until I was around 23 or 24, although I read
Dirk Gently's Holistic Detective Agency as a teenager. I'm not sure I'd use it as an introductory novel for science fiction, as although they're fun, I'd suggest the first two Red Dwarf novels as better options if you want to ease someone in via comedy SF (although that may be particular to my age group as I grew up with the TV show - used to sneak downstairs as a kid, hide behind the sofa and peek round to watch it because it was after bedtime).
The rest were all (with one exception) read during my early to mid-20s -
1984 and
Fahrenheit 451 were bought new with a gift voucher because I decided I had to read them, everything else was a second-hand find, in individual volumes excluding
Electric Sheep which was in a single volume also containing
The Three Stigmata Of Palmer Eldritch,
Martian Time-Slip,
Ubik and
A Scanner Darkly - not a bad find for £3. The one exception was
Slaughterhouse 5 - I've still never read it and don't currently have any plans to do so (the only Vonnegut novel I've read was
The Sirens Of Titan and it disagreed with me, although I can't explain why I disliked it to the extent that I did)
I'm not sure which I would recommend to new readers - at the risk of stating the obvious, it is too dependent on current reading habits and their general age group. I feel that
Dune and
Hyperion are better options if someone is familiar with fantasy (they could be argued to be "space fantasy" in a sense themselves);
Ender's Game may work for younger readers (I was in my 20s when I read it though so that's not something I can speak from experience about); I'd pick
Brave New World over
1984 and
Fahrenheit 451 for the classic dystopias as I thought it worked best as a novel (despite
1984 being the one whose terms have seeped into general consciousness) although it feels a little dated; and
2001 (along with
2010 and
2061 - I didn't like 3001 and felt it was an unnecessary extension of the series) for people who just want to read about people in space. I wouldn't ever recommend
Stranger In A Strange Land to anyone if they haven't read it because I don't think it's a very interesting book - either Heinlein's juveniles as an introduction to SF (though a lot of them are dated) or as mentioned earlier in this thread,
Starship Troopers or
The Moon Is A Harsh Mistress (the latter being my favourite Heinlein novel as the lead character is surprisingly engaging once you get past the narrative style) are far stronger options.
*Except 'Friday'. I liked 'Friday'. Sue me.
So did I - I felt that
Friday actually had a relatively interesting world and a reasonably engaging plot - it was preachy (as all Heinlein apart from the juveniles are, and even then there are undertones of preachiness...), but I also thought it was quite an enjoyable book. As for my opinion of the other late Heinleins... basically a vehicle to express his admiration for incest and an attempt to tie as many old books into one multiverse as possible.
