The John Carter series. It layer out the prototype for the modern Super Hero.
Those "barsoom" stories were some of the first novels I ever read. I'll have to re-read, and see how they hold up. Also from that time-frame, and also superhero prototypes, were his "Tarzan" stories, and the "Doc Savage" pulp novels (not sure who wrote those).
When I first got an ereader, I downloaded them from Project Guttenberg and gave them a good, honest read. They didn't seem all that aged to me and I thoroughly enjoyed them for being simple and straightforward. The swashbuckling scenes especially were a lot of fun. Since we are talking pulp sci-fi and easy reads, if you never have, see if you can find any Tom Swift novels. You can usually pick one up at an atique shop for about $10-$20. They're not what I would call good, but they definitely carry a feel for the time they were written in. Edit: I haven't read any Tarzan or Doc Savage, but I might seek them.out if you think they're worthwhile.
I remember reading one or two of the "Tom Swift" books, vaguely. It's been a long time! These (along with several Jules Verne tomes, my grandmother had a collection) were the first "grown-up" books I read.
Yeah, the Tom Swift books don't actually hold up all that well, so don't go into them expecting something great. They're fun to read though cause they're a part of pop culture much like Nancy Drew or The Hardy Boys. Speaking of, I see that a lot of the old Gold Key comics such as Turok, Solar, and Magnus were recently republished and I'm a bit tempted to get a few just to check them out. Sadly, they seem to be a bit on the expensive side so I wouldn't be able to justify getting them all. I haven't read any Jules Verne, but I think Arthur Conan Doyle was a contemporary of his and I did read The Lost World which was a lot of fun, though I don't remember much of it.
Verne is not an easy read (as I recall) - the language is a little bit dated, and Dickens-ish, sorta? But I remember enjoying "The Mysterious Island" very much, as a boy (back in the 1970's).