In many senses, this is everything I ever wanted from a roleplaying game: fantasy, alternate history, steampunk and pulp qualities, sci-fi, world exploration and so on.
The idea of exploring alien cultures within our own solar system, flying steam-powered ships between the planets, hunting dinosaurs in the swamps of Venus, defending the British colonies on Mars, is the stuff gaming dreams are made of.
Unfortunately the rules mechanics are very clunky and archaic - which is a shame, because the game has incredible support material available for it (particularly in the form of the Transactions of the Royal Martian Geographical Society books) that make you realise its enormous potential for long-term campaigning (always a point of personal importance to me when selecting a game).