The books were often pure escapism and the characters tend to be a little flat but if you judge them for what they are they are not bad books. Most of those classics could not be published if they were written to day but that is true for most classics. Some o these works have been copied some many times that they seem less original when you read them.

Heinlein and Asimov have similar styles and are very different Dick and Bradbury who are both fairly unique and tend to explore reality more than science. Clark is old but his writing style is more modern and fits in better with writers like Card and Niven.

If you don't ant to jump to far back read Mote in god's Eye or if you want a more classic style trying reading The Puppet Master but keep in mind this was pulp fiction and they had to write two or three of the books a year to stay fed. They are not as refined as modern novels.