Let me begin this review by saying that I have not played Nine Worlds at this time, and I will mainly comment on the production values and the creativity of the game. As such, I cannot comment on how balanced the various mechanics are. I can, however, comment on how it is an excellent read and well worth your time and money (especially considering that is currently available for free).
Nine Worlds is, at a glance, not highly original. The influences of Mage: the Ascension are fairly obvious, as well as those of Michael Moorcock's writings. However, it is not the dark fantasy those influences would appear to imply. In fact, the stories it tells are largely closer to light-hearted pulp fiction, with an eye towards the wonders of magic and science. In Nine Worlds, the players assume the roles of Archons, people with extraordinary talent and influence over fate thrown into a larger world of godly beings and their conflicts. The science of Earth is mostly a weaving of fiction and truth, but the powers of Archons and other potent beings of the Nine Worlds (Earth, Sun, Moon, Mercury, Venus, Mars, Jupiter, Saturn and Hades, from innermost to outermost) largely trump the knowledge of science. Archons are told about the truth by Prometheus, the titan ruling over Earth, and left to their own devices. In this newfound realm, they forge tales and melodramas of demigods, until they find a task that they can claim to be their last, or their legend is prematurely ended by death or oblivion.
Nine Worlds uses playing cards for conflict resolution. As someone who likes playing card games, I have often found the use of playing cards in tabletop RPGs a gimmick, rarely worth replacing dice or diceless systems with. Nine Worlds is a refreshing change of pace in this regard. Each PC has three groups of stats: Virtues, Urges and Muses. Each player also has a deck of playing cards, Jokers included. There are two Virtues, which determine how you approach (with mortal skill and luck or with supernatural displays) each conflict and the general status quo of the Nine Worlds, as well as how many cards you draw in a conflict, and four Urges, each of which correspond to a suit of cards and have their own powers (creative, destructive, transformative and static). These remain largely static, and while they can be improved, this does not happen as often as altering the Muses. The Muses are each tasks that a PC can accomplish and contains enough dramatic conflict. Throughout gameplay, or even a single conflict, these Muses will rise and fall in value, and they add cards to a player's hand and determine how much and in what ways the PCs improve when resolved. In its most basic, the players draw a number of cards from their deck equal to the ratings of their applicable Virtue and Muses summed up, see how many cards you have of each Urge's corresponding suit, and add the Urge's value. If you beat your opponent's number, you get to determine how the conflict ends. The players also have many ways of influencing these values, but the basic system remains the same. If one of the player's Virtues is reduced to 0, he can sacrifice a Muse or accept death. If he has no Muses left, he automatically dies. The character sheets have little room for customization, so the tasks the PC has as his Muses become the main way of determining what the characters are about. As a result trying to powergame the system is largely a narrative affair.
The setting itself is largely minimal in its mechanical influence, but it is also well-written, well-detailed and well-suited to modification. The backstory of the Nine Worlds is a retelling of the war between the gods and the titans of the Greek mythology, with the personae and the details modified to fit the game. Archons are the spanner in the works of the scenario, their influence determining the ultimate fates of the Eternals and the titans. While an Archon might not want to be involved in the melodrama around them, the nature of their Muses ensure they will be drawn into the thick of things. Several of the prominent figures in Greek mythology also get the Nine Worlds treatment, but many are left to the game master's discretion and imagination. If, like me, you are not a big fan of pre-written settings, the game mechanics are also suited to creating your own epic melodramas, but the setting is worth a read for idea mining, at the least.
Aside from the cover and the page decorations, the presence of artwork is largely minimal. While you do not necessarily feel their absence, as the artwork is mostly black and white and not always evocative of the writing, it does lead to the book being a bit sparse. Still, the artwork that does fit fits very well, and the writing largely carries the book well enough on its own.
For a free game, Nine Worlds is of undeniable quality, and worth giving a shot. For me, it does not compare to such games as Unisystem, Mutants & Masterminds and the major influence on the game, Mage: the Ascension, but I did have fun reading it, and I believe I would have fun playing it. It does have several assumptions in its mechanics that prevent it from becoming truly universal, and thus might not be suited to every group. But if you like epic stories, if you like melodramatic narratives and if you like pulp fiction, you will not regret the time you spend on Nine Worlds.