Just received my copy of Warriors of the Red Planet a couple days ago and tore my way through it. Even though it's only a beta, I'm really impressed with it. It's flavorful, succinct, and has my imagination kicking in. As a fan of the Sword & Planet
genre, I feel they did an excellent job of boiling the ideas down to their most basic level while tweaking the OD&D rules to perfectly fit the concept. While I may end up converting it to Mini Six for familiarity, I see no problem with the rules as presented.
There are 4 basic classes: Fighting Men (Fighter), Scoundrels (Thief), Mentalist (Psionicist), and Scientist (using weird science instead of magic). The book includes numerous powers and gadgets for the Mentalist and Scientist classes. A fifth class, Sorcerer of the Black Gate, is added in an appendix and presents an optional magic system. Swords & Wizardry is recommended for expanding the magic options if the Sorcery aspect is used, which I assume means the rulesets are very similar.
While most of the book seems geared toward the John Carter of Mars series, it also provides instruction on creating new planets from scratch, along with numerous random charts and tables to assist with this task. A lot of the advice centers around defining only basic details and filling in the rest during gameplay (a tactic I prefer).
All in all, a wonderfully creative retroclone that perfectly adapts the rules to fit its target genre.