Ellis and Cassaday take this notion and run with it brilliantly. The first few issues introduce the main characters and lay out a few mysteries. We get we get a series of revisits to things which the world considers fictional - Doc Savage, Japanese monster movies, Tarzan, "Them!", and so forth. Names are changed
Don't be misled by the fairly independent stories of the first part of the run, it's a series that demands and rewards reading in the original order. Skipping the second collection and reading the third would be a major mistake.
By the middle of the second collection the backstory comes more and more into the foreground. Even as it does, the series continues to revisit tropes and stories we've known and loved, though less often. The long-form story concludes in a satisfying series of events, and an additional story serves as both epilogue and emotional resolution.
Through the entire run Cassaday displays a pretty amazing ability to incorporate the style of bygone artists and authors while giving the reader something that does not jar visually - except, of course, when it's supposed to jar. (The Batman crossover is especially good on that point.) Similar attention to detail and swings in style are accomplished by the colorists and letterers.
Cassaday and Ellis clearly know their material, and wrap the old and new together in a way that resonates visually and emotionally for the reader. A chunk of the fun is seeing their take on these stories, and yes, if you don't know what they're riffing on you might not enjoy that segment as much. But even the ones that went by me on first read were enjoyable and coherent, and since them I've found much of the original material. On this re-read I enjoyed them even more.
In short, I highly recommend PLANETARY. Buy the first trade paperback; if you're not hooked at that point you're not going to enjoy the other three. If you are hooked, you'll probably want the Batman crossover Night on Earth. With respect to reading order Night on Earth and the other specials carefully presented such that it could take place pretty much anywhere after the first trade collection. Night on Earth was and is one of my favorite "done in one" comics and is still in print. The other two specials are not, and for good reason. In missing them, you're not missing much.