About seven years ago I decided to start re-locating some of the books I read growing up so that I could re-read them as an adult and compare my understand and feelings about the books to what I felt as a "tween/teen".
It has been an enlightening journey to be sure.
There are some books (Stranger in a Strange Land and Dune) which I simply could not wade through as a young teen which I now read with depth and understanding, and in some cases a little awe that the writers could construct such a story.
Other books were good then (with a teen's understanding) and I enjoyed them even more now with an adult's perspective (McCaffery's PERN series, David Drake's "Hammer's Slammers" series, selected Bradbury)
Some books (the "Pip and Flinx" adventures by Alan Dean Foster, and the "Castle Perilous" series by John DeChancie) remained light, fast, adventure reading but have aged very well and were as enjoyable to my adult self as they were to my younger self.
Then there were some disappointments, for example The Space Mavericks by Michael Kring. I LOVED this book as a teen and as an adult it seemed so...thin. "The Last Rangers" series by Jake Davis. Again, like eating a cream puff, maybe a little too much flavor and not at all filling
Still it's been enormously educational and I've enjoyed the nostalgia as well. I feel this project has been time well spent and I've learned a LOT about myself and the ways I've changed over the years from doing this.
"Castle Perilous" series and the "StarRigger" trilogy by John DeChancie 
"Mad Amos", "Codgerspace", "Pip n' Flinx series" by Alan Dean Foster
"Sten" series by Allan Cole and Chris Bunch
"Bolo" books by Keith Laumer (and later others)
"Hammers Slammers" series by David Drake
The "Dancing Gods" books by Jack Chalker