I read the rules part for complications during Missions and the choice for adding extra/harder Adversaries mentions that using a Daemonhost or a Tyranid Lictor would be a good choice. Sounds fine except neither are in the rulebook. So here we are again. I don't understand this at all. The rest of the book goes into such detail with all sorts of cool stuff and yet the section on what the Space Marines have to face is almost an afterthought.
So if I want Daemonhosts I need to buy an entirely separate game, Dark Heresy (which I'ms ure is great, but not really the point).
And if I want Lictors I need Creatues Anathema, which is £27 for 3 pages worth of info.
On top of that, while I'd love to own those books I notice that the entry for Lictors (having browsed it) is fairly hefty. Now in play this means i'm going to need to either know what all his many (many) talents and traits do by heart, or I'm going to need to cross reference with the main rules. The game is already fairly detailed and the books already fairly hefty. What if i need further info? Daemonhosts will have their own rules within Dark Heresy and cross referncing that and Deathwatch at the tabel (along with whatever other books i might use, such as Rites of Battle) is getting crazy! That's on top of the steep learning curve - i'm sure it's great once you know it.
Finally there's the problem of balance: using the Lictor as an example Dark Heresy is scaled at a third the power level, initially, that DW is. That's the difference in character power levels, using XP as a guide (I don't know how else you'd do it). Lictors are presetned as enemies for Acolytes. I have absolutely no way of judging how tough a Lictor is compared to a Space Marine (or indeed anyone, since there doesn't seem tobe any objective explicit measurement system and I have no idea how many xp was used to build the Lictor). They look tough, but compared to what? If i set a single Lictor against a Kill Team will it mow them down like grass or go down like a sack of spuds? On top of that I have no idea what the average Kill Team is supposed to look like, in terms of numbers. The average gaming group is likely 3 or 4 (i'm not sure DW could work with a two man kill team but that's beside the point) so how do you guage threat sizes against player numbers as well as XP levels?
Don't get me started, you didn't mention a "good" RPG