So I started talking about how skills help to define a game, and I never finished. Here's another bit.
Deathwatch has a very extensive list of skills. There are no less than 60 listed on the character sheet, of which 11 are sub-skills of a group and many further sub-skills aren't listed. Ignoring the groups and allowing for the extra sub-skills, there are probably around 80 different skills in the core game. Admittedly three or four of these don't, in fact, exist - the character sheet notoriously includes skills from previous games in the game line that aren't covered in the rulebook itself. Never mind.
What do you do?
Looking through the list of skills, you can get a few basic impressions. One is that this is going to be a relatively actiony game; there are skills for knowing about War, Demolition, Dodge, Shadowing and Tactics. Despite the fact that social skills appear, you probably won't be spending your time dallying with socialites. That being said, there aren't really any skills for actually fighting. Does this mean you don't fight in this game? It seems unlikely, considering the other skills that exist.
The main focus of Deathwatch is, in fact, fighting, and that's why there is no skill for it. Weapon Skill is an attribute, rather than a skill you learn, and it behaves somewhat differently in terms of advancement. You can improve your ability with specific weapons using Talents. A fight involves a combination of Weapon and Ballistic Skill, your Dodge ability, Tactics, Command to influence your team and allies, and occasionally application of other skills like Forbidden Lore to recall enemies' weaknesses, or Acrobatics to perform unusual manoeuvres.
However, there are still a significant number of skills that deal with social interaction and knowledge, with observation and investigation, and with stealth. This suggests that it's not a hack-and-slash game, but one where you will need to interact with NPCs, gather clues, and make sensible tactical and strategic decisions about how to proceeed with your aims. The number of skills touching on these tasks implies that there will be a fair amount of depth to these aspects.
This is actually misleading. As a Space Marine, you are enormous, easy to recognise, and worshipped as angels of the divine Emperor by most of the population. You do not blend into crowds. Moreover, your extensive training in the arts of war have left little room for any kind of people skills, no detective training, and a positive mistrust of technology or magic. Generally speaking you expect to be dropped at high speed onto the surface of an alien-infested world, not asked to solve locked-room mysteries. There is a certain amount of clue-gathering as you look around suspicious sites, sneaking quietly into hostile territory and talking to untrustworthy planetary governors, but these are relatively minor. It's also very difficult to gain any competence in these skills (partly because of their limited use), but that's a separate issue. In practice, the skills seem to primarily exist because they were used in other Warhammer 40,000 games in the same system, which did have a much heavier investigative focus. I suspect they could reasonably have been dispensed with for Deathwatch.
Many of the skills are non-intuitive, or at least unclear. It's not immediately obvious what Carouse is for - is it for getting on well with others? Evaluate is presumably for judging the worth of items, since there's a Trade skill later and Barter for haggling (why are they different?). Inquiry? Performer seems odd in a game about space warriors... and what's Psyniscience? There's Invocation, so that must be for casting spells, so presumably everyone can learn magic, right? And there's Scrutiny, which is different from Search, as well as my Perception attribute. Security? Wrangling?
Carouse is, in fact, for determining how much alcohol you can hold - a vital skill in battle, no doubt, particularly since Space Marines are essentially unpoisonable anyway. Evaluate does let you judge the worth of items, but its significance for Space Marines is in helping you find weak points or discern the best available cover. Trade represents craft skills. Inquiry is chiefly for picking up news and rumours. Security is hacking and lockpicking. Wrangling is animal handling. Only Librarians can use any form of psychic ability, so those skills are irrelevant to others.
In fairness, several of these skills are unclear because they'd typically either be bundled into a single broader skill, or spread across more than one skill. Security includes breaking in, scoping out buildings and hacking locks (but not other tech), which another game might distribute across a stealth or physical skill, a mechanical skill and an observation skill. Evaluate is a highly unusual combination.
A potentially more useful impression you'll gain is that this is a relatively crunchy game. There are fine distinctions between some skills: Perception vs. Scrutiny, Silent Moves vs. Shadowing, Security vs. Tech-Use. Some skills have multiple specialities within them. Some skills are limited to particular "classes", and there are plenty of things that can't be tried at all without buying the training. As you might predict from a game that's crunchy in this regard, Deathwatch is also relatively crunchy in other aspects, such as injury rules, having a large array of similar weaponry to choose from, degrees of success and so on. However, there's relatively little tracking required in play, not too much in the way of exceptions and subsystems, and it caps realism in favour of a somewhat dramatic style.
You can also judge that unless the GM brings modifiers into the equation, you aren't particularly competent at anything, as your stats hover around the 40 range and it's a percentile system. There are a few constant bonuses listed on the character sheets, enhancing your Strength and Perception, and several bonuses may apply to attacking things; the general result is that you're pretty decent at actual combat, and fairly rubbish at most other things. This combines with the low frequency of most skills, meaning it's relatively unusual for you to successfully use any given skill in a game. Skill advancement is mostly limited by your tier, so there's very little you can do to change this early on. Sticking to combat really is your best option.
I think Deathwatch is a mixed bag as far as the skills list goes, and particularly the character sheet rather than the actual skills chapter. Because of (I assume) a desire for consistency across the product line, there are a significant number of skills included that have very little place in a typical Deathwatch game. These give a false impression of the likely importance of covert ops and other non-combat skills, and thus the type of experience you can expect. While you can deduce and reinforce that it's an action game with a fairly crunchy combat system, you may be expecting Mission Impossible when you're basically getting Ultramarines. You can up the thriller element somewhat, but low competence and some setting issues are likely to limit your ability to do so successfully.
Skill names are not as intuitive as they might be, but this is partly a function of the sheer number of skills, and also because of the slightly uncommon way some skills are bundled and distributed. None of the names leap out as misleading.
The character sheet also includes several skills only available to specific characters, and could have been streamlined by leaving these off, with spaces for extra skills to be written in as needed. But that's a fairly minor issue.
On the whole, a reasonable job, but could do better. However, I can understand the desire to maintain compatibility and continuity across the product line by not doing the streamlining that would have probably been necessary. This seems like a case where broader factors conflict with elegance, and since the retained skills don't actually undermine the game, it's hardly an awful decision.