Rogue Trader is the next line of Warhammer 40k RPGs put out by Fantasy Flight, following Dark Heresy by a few years. The system has certainly benefited by the time that has gone by and the work done on the line. It operates with very similar concepts to its predecessor, including a d100 system, a system of spending experience to purchase skills and talents (special abilities) and leveling is based on experience spent, and an articulated character background system based on your homeworld and other background information. The largest changes come in the addition of space-ships and themes of the game.
Chapters 2 and 3 are based around character creation and rules. This game makes use of an "origin path" system for generating a character background. This information has mechanical effects that give you special boons and disadvantages based on your character's life thus far. The book and the Fantasy Flight web page provide a graph they encourage you to use for the entire group to develop pre-existing character relationships and shared interests/histories. This system is quite different form what was provided in Dark Heresy, but ends up with a more articulated and customized character. "Classes" only have one straight path of advancement, instead of the complicated routes of advancement in Dark Heresy. This takes away some customization, but it really is ok. You can still spend your experience to pick plenty of skills and talents. The classes made available include the Rogue Trader, Astropath Transcendent, Navigator (a second psycher), Exporator (Tech-priest), Arch-Militant (Fighter), Missionary, Seneschal (knowledge keeper), and Void Master (pilot).
A chapter is dedicated to Astropaths and their disciplines/powers. It gives some rules for their use and their abilities, and is followed by a similar chapter for Navigators. Anyone playing either type of character will need to go through these sections at character creation. There is some additional background information to be dealt with here, that has a mechanical impact on your character.
A major departure for this game comes in its monetary system. Rogue Trader creates an attribute not unlike strength or agility called Profit. This attribute is rolled like any other attribute to see if the character can acquire the new item. It is modified by rarity of the item and your location when trying to acquire it. This system is a major boon to the system since the game does stress how much money is actually flowing through your hands. It feeds the idea that you have people to keep the books for you. The rules are not exceptionally complex, and work well, but you might just not be able to get that new storm bolter even with a very high profit.
The section provides some base templates to build from, and at character creation the number of build points you have for your ship is determined (there is a chart that gives you a starting profit and ship points in an inverse manner: the higher your starting profit, the fewer ship points you get). These build points let you get a bigger and better ship. The templates that are provided range from small merchant ships to navy cruisers.
The information of background for this game is of similar design to what was in Dark Heresy. There is a chapter dedicated to detailing the universe in general and the Imperium of Man in specific. The following chapter gives great details on rogue traders and their place in the universe. These chapters can help players not familiar with the setting and have a desire to make their characters more connected to it. It would be a good idea for anyone to read through this of course, even if you are an old fan. There is always information of the Kronos Expanse (the actual setting of the game) that could be of use.
The game is incredibly easy to set up and run as a one-shot game if you have nothing else to do (say your weekly game will be missing a player and you still want to play), and it can also benefit from campaigns. The character creation system is designed to be done as a group activity, and the game certainly expects players to operate as a team. The rules are fairly intuitive, but do require the book or print-offs on hand at all times (see below). Difficulty of tasks and rolling is handled well, where you roll a d100 and try to get under your attribute (which is modified by conditions and the difficulty of the task). The system is a great deal of funwhen you have all the information you need on hand. A lot of the art is beautiful, and evokes the feel of the game, especially in the early chapters. Character images are especially well done in the class chapter.
What keeps this game from getting 5 stars is a problem that existed in Dark Heresy that continues on in Rogue Trader (and will likely not be fixed any time soon). You need to constantly be ready to reference a large number of charts to determine a number of issues, including difficulty modifiers to rolls, critical hit results, and so forth. This can severely slow a game down (especially in combat). You will need to have ready access to all these charts on a regular basis when playing the game. It also is in need of an errata, as there are a few typos (which is disappointing considering how long it took for the game to finally ship and how long it took to publish). Some of the art is not as sophisticated as would be expected. Ship images are especially disappointing. Considering the incredible gothic structures that act as ships in this universe, the seemingly poorly designed computer images of ships does not evoke the ancient and foreboding feel vessels of Warhammer 40k deserve. When you expect medieval gothic cathedral and get Babylon 5, you are bound to be disappointed. Other art that is not as pleasing still fits what has been done for Warhammer 40k, but still might not appeal to someone new to the setting.
Overall, I can say I enjoy the game. It is an improvement from Dark Heresy, which was itself an excellent game. This seems more playable to someone new to the setting, and gives people an entrance to Warhammer 40k for people that have previously not been interested. It is certainly worth picking up, and can only get better with supplements, though none are really necessary to really get into this game. I could not ask for much more in a game.