I hadn't seen any of these episodes set in WW2 prior to buying the DVD and it was well worth it. I've now watched all the episodes on this set and am onto Season two. Now that I'm watching the second season, I find I miss Diana's innoncence and the close relationship that was developing between Diana and Steve from season 1. It's not the same in season 2 because it's steve's son. Also, in season 2, Diana seems more world weary.
Definitely watch season 1 first! It's such a great way to escape from the humdrum of daily life. Of course, there are many silly, dated, nonbelievable, and campy aspects in all shows (including the theme song lyrics: "in your satin tights, fighting for our rights"), but that's part of the fun of watching Wonder Woman. Enjoy!