Three years ago, Shaenon K. Garrity wrote a wonderful recommendation of the title, complete with lots of art. Her Overlooked Manga writeups are always worth reading. She also points out that, although Keiko Takemiya is best-known as a shojo writer (manga for girls) and this series definitely is shojo-flavored, this title originally ran in a shonen (for boys) magazine. Then she goes on to provide a loving art analysis:
Outer space, oppressive futuristic societies, mutants, ESP… is there anything science-fictional this manga doesn’t have? No. There is not. And Takemiya’s art is just about crazy enough to handle it. There are times when the storytelling gets a mite confusing, especially when there’s telepathy flying around, but it always looks fab.
As the above examples illustrate, To Terra looks so Seventies you can hear the Fleetwood Mac playing in the background, and in my mind that makes it perfect. I hell of love 1970s sci-fi movies where everything is made of molded plastic and softly diffuse light, whether you’re talking about 2001 or Soylent Green. Anything with womb chairs rocks out. Takemiya fills her world with almost whimsically curvy, patterned, organic-looking technology and architecture, and she incorporates the style into her page designs as well.
If you’re looking for a more substantial art sequence, instead of selected pages, check out this archive post from Christopher Butcher with a 16-page section from the first book. (If you have trouble finding it on the page, just search for “Terra”.)
These two should give you a better idea of what we’re talking about when reviewers mention the “classic” look.