I grabbed the iPad Deathwatch codex.
One of my buddies voiced concern it made other marine codexes redundant, had material form other codexes and did it all.
Obviously he has had a enough of GeeDubs but I thought I'd point out what is in the Deathwatch codex, for the purposes of clarity and not spreading fud.
Comparison to other marine codexes
It is similar to space wolves in the sense of being able to put wolf-guard terminators in powered armoured groups, but that doesn't seem to be a regularly abused rule. What space wolves have is the frost-cannons, packs of wolves and sagas. All of which seem to be used and abused by wolf players for me to feel they are mechanically sound. That's what sets the codex apart- and deathwatch don't get any of that.
It makes use of deep strike like blood angels, but doesn't have the accuracy, nor 2+ save jump pack troops. They can get 6+ feel no pain, but no apothecary.
They can get 4+ invulnerable as a relic but only if the unit doesn't move (not like the dark angels).
They get tactics like ultra marines but not as good. Choose army wide to get re-roll 1's to hit HQ choices? or fast attack? etc um, yeh ok, not as good as the ultramarines tactics, not awesome.
So they do a have a lot of abilities that are similar in feel to a lot of different codex's, but not quite as good mechanically or flexible. They also pay over the odds for the basic guys. 40 points instead of 35 for fearless terminators. Before crazy equipment upgrades. When your single wound heavy weapon trooper costs the same as a 3 wound space marine captain you are spending your points wrong. IMO
4 points extra for jump pack vets, 3 points extra for bikes etc.
The formations are ok, but what they enable you to do is build small teams to take out heavy choices, or fast units or HQ units or troops. You might put put a lightning claw terminator in the anti-troop unit, for example.
What the codex doesn't have is tanks- it has transports.
It is also short on ways of dealing with 2+ saves and AV 14 outside of melee.
Zero anti-air outside the flyer it's self.
The flyer is really a better looking storm-raven (about the same points) which can't carry a dread but can carry bikes (not sure if you can put bikes in a raven?)
TL:DnR- it doesn't make any of the marine codex obsolete unless you only fielded ultramarines sternguard in drop pods and stormravens and a calling it an army. It does a better job of that.
Grey Knights in the back of Slaves to Darkness - the original source, before the grey knight terminators, was a chapter, described in the same scale as Emperor's children, black legion etc. More librarians, access to nullrods, psykout grenades in their missile launchers etc. I didn't like the 5th ed version that was their glory days, where the fluff said losing 100 was apocalyptic. Well, the old version it is no more disastrous than it is for any organisation of 1000 soldiers.
Deathwatch in the rpg fluff have been small squads, and certainly they have always talked about teams. But if every chapter tithes a dude that makes a full sized chapter. Does it make sense for 200 of them to end up somewhere. Probably not any more than the idea that there are less than a 1000 Dark Angels, Blood Angels or Ultramarines. And you can certainly fit a full company (100) of them in a tabletop force.
I have more of an issue that you could use deathwatch against imperial guard or other spacemarines, or use ultramarines against ultramarines in a tournament..it's simulated combat..right?.
Where they fit
What do deathwatch do well? Kill infantry at medium range with especially 4+ or worse saves. They aren't going to wreck khorne in close combat. They aren't going out shoot tau. They aren't going to out-last necrons, and they certainly aren't going out-manoeuvre eldar.
Think of them as just wolfguard as an army (but no access to packs of wolves, wolfriders, longfangs or super-dreads). This might mean you ally the hell out of them. Imperial guard could provide cheap bodies and armour, both of which they lack.
What I like
Army wide infantry deep-strike. Sneak, drop pod, teleport, HiLo, I think it all suits the Deathwatch Modus Operandi.
Minis : I means some just look good but some of them are spectacular.