With so much going on in multiple new (or updated) codices, and with a lot of focus on different weapons (e.g. like the DW Frag Cannon and the Genestealer Cult Metamorph weapons), I think that the humble Deathwatch Veteran squads have been somewhat overlooked, especially with their access to DW Special Weapons. Specifically, ANY Veteran in the squad cam replace his Boltgun with:
-DW Shotgun (Free)
-Stalker Boltgun (1 MB)
-Flamer (1 MB)
-Meltagun (2 MBs)
-Plasma Gun (3 MBs)
-Grav Gun (3 MBs)
The ability to take up to 10 Special Weapons per squad is pretty good in and of itself, but what really sets this apart is the fact that each Veteran can replace his CCW with a Bolter (that can use the Special Issue Ammunition) for free. That means each Veteran can have a Bolter AND a Special Weapon, giving them tons of versatility and making them significantly better than an equivalent SM Sternguard with a Combi-Weapon.
Taking a look at each of these Special Weapons in the context of the Deathwatch army as a whole, here are some thoughts:
 Flamer — While the DW have plenty of options in dealing with hordes, the ability to take up to 10 Flamers per squad (and still have Bolters for longer-ranged engagements) can be quite devastating, especially when paired with a Drop Pod or Rhino/Razorback, to set up optimal Flamer “firing lanes” as the unit disembarks. These obviously complement Infernus Heavy Bolters quite well, since that adds more Heavy Flamer templates (to supplement the normal Flamers) and long-ranged shooting (to supplement to the Bolters), giving you a very potent unit against light-medium infantry.
 Plasma Gun — Though this can get overlooked a bit because of the other Special Weapons, Plasma Guns are actually quite versatile, being able to deal with ALL kinds of infantry and also light-medium vehicles. Their big disadvantage, Get’s Hot, also can be mitigated by Deathwatch armies, thanks to re-rolls of 1s to Hit from the “Mission Tactics” special rules, making them much less dangerous than when used by other armies. I actually think this can combine quite well with DW Frag Cannons, making for LOTS of S7 shooting against vehicles and also very solid anti-MEQ/TEQ firepower as well.
 Grav Gun — Obviously, the go-to weapon for killing most MCs and Heavy infantry, as well as a decent tool against vehicles in a pinch. Without Relentless on the Veterans and with no Grav Amps for re-rolls, this is obviously not as powerful as, say, Grav Cannon Centurions or Grav Cannon Devastators in a Skyhammer Annihilation Force, but I think they still have a definite place in a DW army, especially since the Veterans can use their Bolters/Special Issue Ammo against any targets that the Grav Guns are not effective against (i.e. light infantry, units in cover, targets greater than 9″ away if the Veterans have moved, etc.).
 Melta Gun — This one is a no-brainer, being the best weapon against heavy vehicles/Super Heavy LOWs and also a strong weapon against multi-wound T4 models (like Wulfen) that are vulnerable to ID from S8+ shooting. Like all the other Special Weapons, it is significantly better in the hands of DW Veterans when they also have a “free” Bolter with Special Issue Ammo strapped to their backs… if you kill a vehicle on your first turn arrival, you then have the versatility to switch to the Bolters if your melta weapons are not as optimal against the remaining enemy forces.
 DW Shotguns — One of the “new” Special Weapon types, this is a very versatile option that can put out lots of wounds with Cryptclearer ammo (thanks to S4 and Shred), can take down enemy with 4+ armor or worse before charging with Xenopurge rounds, or can use Wyrmsbreath shells to, in essence, give the entire squad “free” Hand Flamer templates. Like everything else, the ability to combine all these options with the four different Bolter Special Issue ammunition types makes DW Veterans amazingly versatile, especially since a Veteran can take both a Bolter and a DW Shotgun for free (i.e. only the base 22 points per model that they normally cost).
 Stalker Boltguns — This may actually be the “crown jewel” of the DW Special Weapons, with the ability to engage targets with 2 Sniper shots a turn per model at between 24″ and 36″, depending on the ammo, and also do everything from Ignore Cover (Dragonfire Bolts) to Ignore 3+ Armor (Vengeance Bolts) to always wound on a 2+ (Hellfire Bolts). Add in the “quasi-Rending” of Sniper weapons and you have a genuinely potent, long-range Special Weapon that can devastate enemy-non-vehicle units at stand-off distances (especially with the help of Mission Tactics and Doctrines from different Kill Teams). The primary weakness of the Stalker Boltguns, their inability to move and shoot, is mitigated by the option to have both a Stalker Boltgun and a normal Bolter on every DW Veteran in a squad, thus giving them the ability to engage a whole slew of non-vehicle targets at various ranges with great efficiency.