Ok, I just started my own game for this system after grabbing the books thinking they would be good source material for the Dark Heresy game I was running... because Death Watch looked so cool it made me stop running a game to run it.
You would think a game about being a nigh invulnerable paladin in the service of the Imperium would be boring, or at least boring to people that don't do war games, but the writers managed to do an incredible job of expanding on the established lore to make the inhuman warriors of the astartes more human-ish. From the first chapter they emphasis the differances between the chapters, how the varied homeworlds can affect the culture, and the rivalries between the differant chapter houses to bring these giants down to eye level, examining everything from the view each chapter has of the emperor and it's own primarch to it's combat doctrine and rituals. You never quite lose the awe the setting is meant to inspire but you do get a better feel for the inner workings of your own marine's mind as you make a character. That leads us to the crunch of character creation, the system is meant to be compatible with the other WH40K rpg books and the core system is, even if your rogue trader or inquisitor needs a lot of experience to stand tall in the situations a death watch marine is called in for.
Right out of the gate you have the option of two differant ways of generating characteristics and the charts for developing the signature moment in your character's past as well as the history of his armor are fun mechanics, and chapter trappings is a fun way of adding further color while giving some interesting, small, specific boosts, each chapter house is well defined with it's own positive and negative traits and the specialties that replace DH careers are, for the most part well defined, each with their own role. Apothecaries are battle field medics and very good at it, according to build they can protect you from mutation, create poisons to augment the offense of their battle brothers, or heal huge amounts of damage. Assault Marines are, because of their jet pack, highly mobile close combatants able to spearhead a charge or move around the battlefield and their special abilities allows them to bring the hurt to hordes(more on hordes later). Devastator Marines are heavy weapons experts able to affect the field of battle through direct or indirect damage, out of the gate they have the highest potential damage output and are fairly straight foreward to play, "stand here, maybe use cover, shoot things", they take the place of the ranged fighter from D&D or the heavy weapons specialist from Shadowrun, you might not always need that storm bolter cracking away, but when you do you will be glad it is there. Techmarines are fairly self explanatory, they work with machines, augmenting or repairing their function, like apothecaries they aren't bad in a fight but their roll is primarilly support, they do have progression paths that make them in to a battlefield control type, fun concept, well executed but not an easy character type to just pick up. Librarians are, unlike what you may think from the title, scary, they are combat psykers capable of using their mental powers in a variety of ways, from damaging the enemy to coordinating and buffing the group to causing fear effects, it is of course best to specialize but you can get some good mileage picking and choosing specific powers as a generalist, like the techmarine it is conceptually cool and solidly made but a little difficult to get in to from the start. Damn... that leaves only my least favorite specialty, the Tactical Marine... really not a bad specialty per se but it is such a generalist design it doesn't stand out at all, they get some command based abilities but since they lack any real strength outside of that they come off as a something of a compromise between a support and front line combatant that isn't a hindrance but isn't much help either unless you have a bunch of npc's acting in support. Tactical Marines do have a very broad skill selection that is both a positive and a negative since it allows you a lot of choices but it also feels like an invitation trap for spreading yourself too thin. Really I wish they would have held back on this specialty, taking the time to define it a bit better with some better morale boosting abilities and released it as an advanced specialty in Rites of Battle.
In terms of game play Death Watch shines at hard and fast fighting mixed with tense recon missions, there is little room for political maneuvering though as the published adventures show you can design missions with political objectives and as far as weaknesses go it isn't a bad one considering how easilly it can be worked with. The horde mechanic is a fun little in game gadget that lets you take mobs of enemies that otherwise pointless enemies and treat them as one massive creature that can actually threaten a team of marines, with the magnitude, or number of mob members, acting as it's health and helping to determine it's attacks in a round. The enemies treated individually are powerfull enough to pose a real threat and while the game focuses on the heretical Chaos factions, technologically advanced Tau and horrifying mutagenic monster Tyranids with more books scheduled, including a bestiary the game doesn't suffer from a lack of cool baddies, and that is before you get to stuff like rogue or deserter units of imperial forces, common rebels, and criminal gangs. Another interesting aspect is the modes, Squad and Solo mode are, well, like they sound modes of action your marine can be in, in solo mode he is independant of the his team, these modes are determined by your specialty and chapter house, each with it's own unique benefit. Squad mode is, once again as it sounds, acting in cohesion with with the rest of the team and there are a variety of abilities a squad can use in squad mode determined by the the specialty and chapter house of a leader and oath picked at the start of a mission, there are also "general" squad and solo mode abilities and they are usefull, but they tend to lack the flavor of the ones specific to a specialty, chapter house, or oath. In terms of equipment selection all characters have a kit of basic gear they have access to every mission but they also have a pool of requisition points for extra gear, including relic items and services, restricted only by your renown (sort of like street cred in shadowrun, a mechanic to tell you how you are viewed) and your specialty or chapter house in the case of relics and some skill specific equipment. The selection isn't huge, but it is enough to give you options.
Rites of Battle, the first supplement for Death Watch is, basically, everything they could not cram in to the first book, including rules and charts for creating your own chapter house as well as a whole host of new ones more than tripling the count, a system of deeds and honours to make your own character more distinctive, advanced specialties for characters to build towards with new and unique abilities as well as a beautifull, big chapter on new wargear and a whole chapter dedicated to vehicles as well as several chapters of fluff, character hooks, locations and npc's. It's by no means essential but it is one of those books that someone wanting to play Death Watch should have on their list of purchases, and probably within the first 5 spots on that list. A great book, continuing a trend of incredible quality that shows Games Workshop's grubby little paws all over it.
Know No Fear, the second supplement is smaller than Rites of Battle, but only because it is a pure background book, no mechanics, just a history (and a very thorough one at that) of The Jericho Reach, the segmentum of the empire in which a death watch game is supposed to take place, well written with the typically high quality of art work, I like it but I wouldn't scoff at someone putting off buying it considering the low page count and price tag.
The missions I won't go in to detail on here, there are 3 published mission packs so far as well as adventure hooks in rites of battle and a mission in the back of the core book, I will say they are all pretty well done so far, with plenty of options concerning expanding or streamlining them and they are written to give the players choices, solid buys if you want to run something but don't feel solid on the mission creation rules in the books yet and they give a great sense of the setting.
Overall I have to give the Death Watch game line an 8.5/10, there are a few nitpicks I have with it and you can get lost in the maze of options if you aren't carefull but I can't complain about that too much. More people need to buy these books and support a truly top shelf product.