Adamant Entertainment distilled some of the best features of the Planetary Romance/Sci-Fantasy genre into their Mars books. The lineage is obviously Edgar Rice Burroughs, with Green, Red and White (Ape) Martians. There is also a fair enough amount of H.G. Wells, but I have a hard time seeing this dying Mars invading Earth. As they advertise this is not the Mars of reality, this is the Mars that never was. This is Barsoom as it were. While not "John Carter of Mars the RPG" it can be played that way. There are even some surprises in the form of the Grey Men of Mars. Hint, they are not the "Greys" of later UFO mythology.
There are plenty of options for characters with an emphasis on high heroism and great feats. Imagine all the adventure of Victorian Times and the Pulp Era with the feel of a Space Opera in a D&D campaign then you get an idea of what Mars can do or be. This all reminds me a bit of the "Dying Earth" genre as well, since Mars is dying. Maybe that invasion of Earth is not too improbable after all.
I enjoyed this and really want to play a game on Mars now!
[4 of 5 Stars!]