While described as a "Player's Guide" (with the provision of a "Moderator's Guide" for the GM), this book actually contains everything you need to play Blue Planet. Naturally, the other books will enhance your experience greatly, but this is the only one you need!
The book opens with a chapter entitled 'Welcome to Poseidon' and does just that. Poseidon is the planet, reached through a wormhole whose other end is in the outer reaches of our solar system, that is the setting of the game. Being a water world, it's known as the Blue Planet. Apart from a few details on what a role-playing game is, etc., it's written in character, the narrator being a resident of Poseidon who has been hired to make a promotional/introductional recording for the benefit of newcomers to the planet.
A bit of background: the year is 2199, over an hundred years since the wormhole was discovered and the first exploratory missions mounted through it which discovered the Blue Planet. Since those glorious days, things have gone badly wrong on Earth, with the Blight destroying much of the world's food producing capability, and civil disorder on a grand scale. Minor details like maintaining contact with an offworld colony fell by the wayside, and the colonists on Poseidon decided that they'd been abandoned and got on with things for themselves, developing their own ways of providing those items that they'd expected to receive from supply ships. Once Earth began to recover from those dark days, thoughts turned outwards again and ships were sent through the wormhole once more. The original colonists, who now thought about themselves as 'natives,' were none too pleased to have external influences, particularly as those connected with government thought they still were in charge while megacorporations saw Poseidon as a place to be exploited. Things got worse when a substance known as 'Long John' was discovered, a xenosilicate that appears to aid longevity and have other beneficial effects... except to the bit of the planet it's being mined from, of course.
So, the world your players will enter is one with many tensions and issues, as well as the more natural dangers of an unfamiliar environment. I've found that it's best, at least for your first game, to require your players to be newcomers to Poseidon, so that they can enjoy exploring the new setting as well as interacting with the people already there and the plots you choose to throw at them. It's up to you whether you encourage them to read the introduction - there are downloadable copies available, they don't all need to buy the book! - or use it as a guide to your own introduction through role-play and description.
The second chapter gets down to the serious matter of character creation. Each character is described by a range of values for his attributes, abilities, aptitudes and skills. Your attributes are your basic mental and physical capabilities. These may be changed if you choose to have your character genetically modified, or for him to have 'biomods' - cybernetic implants - added after birth. Abilities are things like jumping, your senses and how good you are at picking up languages. Aptitudes, fixed during character creation, are a measure of your innate talents rather than your training - just as some people are good at music, but have never had a formal lesson in their life, for example. Finally, skills are the things you have actually been taught. There are a range of 'training packages' based on your background and career choices. It's not a quick character creation process, but it is one that encourages - indeed, almost forces - you into having a good idea of who your character is before you begin to play him.
Chapter 3 is entitled 'Character Profile' and takes you further into developing the personality and depth of your character. What drives your character? Duty? His faith? A thirst for revenge? Sheer curiousity? What is his usual attitude to those he meets? And so on. You'll also want to come up with a name, and know what he looks like. Next comes a discussion of the sorts of roles that your character might fill - civilian pilot, for example, a scientist, law officer or some kind of scoundrel - with details of suitable training packages to take, what biomods you might have and the sort of lifestyle you'd lead. There are loads of examples and little stories about Poseidon people - flavour text that gives you ideas about what to become, who you might meet and might even inspire an adventure or two.
The next chapter describes the 'Synergy' game system in detail. To see if you manage to accomplish a task, you roll 1-3 d10s, the number depending on your aptitude for the relevant skill. You then compare the lowest number that you roll against a target number, normally based on the appropriate skill and attribute scores you have. The target can be modified by how hard the GM thinks the task is to accomplish, and your aim is to roll less than the target number. OK, it sounds a bit complicated to start with, but once you are used to it it flows quite quickly and is very versatile, as the skills and attributes can be picked according to the precise nature of what you are trying to do, with the difficulty modifiers enabling fine-tuning of the target to aim for. Exactly the same system is used for combat, with initiative being determined by a roll using the combatants' Reflex attributes, and hitting people is a normal task roll based on your competence with the weapon you're using, with a few additional modifiers based on cover, range, relative movement of aggressor and target, and so on. To figure out what damage you've done (if you connect, that is) you roll 3 dice against the weapon's 'damage rating' modified by the victim's Toughness attribute and the value of any armour he's wearing. Each die that rolls equal or under the modified target scores a 'wound level.' That's pretty much it. Once you've grasped that, you understand how to play the game from the mechanics standpoint, although there are a few additional notes on damage from other sources (fire, drowning, etc.) and how first aid and healing work. Combat is intended to be fast and reasonably deadly, and it succeeds in this aim.
Chapter 5: Hardware looks at the equipement available. Being a frontier world, one of the things that careful note should be made of is the sort of power source the item uses, and how easy it is to recharge or fuel it. Kit is sorted by category: power cells, electronics, computers, communications, robotics, sensors, medical equipment and so on through diving gear to vehicles and weapons. There's a lot of futuristic, high-tech stuff here, but it's well-thought out and all sounds like it could work.
Chapter 6 continues this theme with a look at 'Biotech' - including both genetic redesign and implantation of both cyberwear and more subtle biomodifications. For those characters considering adding cyberwear once the game has begun, there are even notes on how long it takes you to recover from the operation!
Chapter 7 takes a detailed look at 'Future History' with a review of events since 2075, when the wormhole linking our Solar System to Poseidon was discovered. The Solar System was already well on its way to being colonised, and so no time was wasted in exploring this new gateway. Upon the discovery of Poseidon, the Athena Project was set up in 2078 to explore and exploit this new resource, and within a few years a full colonisation mission was underway. Unfortunately, this marked what was perhaps the high point in Earth technological cooperation, for not long after the eager colonists had departed the Blight struck. After giving the history of the Blight and its effects, the current state of affairs on Earth and the rest of the Solar System is detailed - good reason, it seems, to up and off to Poseidon if you can! This is followed by a parallel account of what took place on Poseidon, culminating in Recontact in 2165 and its effects on society, technology and the political situation.
Finally, Chapter 8: On The Frontier presents the current situation on Poseidon. The culture and outlook of the 'native' inhabitants, descendents of the original colonists, is compared with that of those people who have arrived since Recontact. The various institutions and corporations represented on Poseidon are also discussed, building up a good picture of the current state of affairs.
The book winds up with a timeline chart, a character sheet you can photocopy and a rudimentary index. (The Blue Planet fan community online has been working on more comprehensive indices to the complete collection of books.)
Overall, it's a fine book with a lot crammed into it, including both a game system and a beautifully-detailed setting. The scientific background of the game designers shines through in the way that everything hangs together and 'works' ecologically and scientifically - it's the sort of place you can really imagine being out there somewhere, just waiting to be discovered!