I have been playing Deathwatch since the new codex dropped for Eighth Edition and in my opinion they are the best Space Marine codex now. Hellfire rounds wounding on 2+ (i.e., special issue ammo) rerolling 1s with storm bolters is brutal. Veteran squads can spam storm bolters which are Rapid Fire 2 which is 4 shots at 12" or less range. They melt away enemy chaff real fast.
Here’s my optimized build for a standard Deathwatch Veteran Squad:
Watch Sergeant - Storm Bolter & Power Axe
Black Shield - Storm Bolter & Storm Shield
Veteran - Storm Bolter & Storm Shield
Veteran - Storm Bolter & Chainsword
Veteran - Infernus Heavy Bolter
Veteran - Deathwatch Frag Cannon
Terminator - Storm Bolter & Power Axe
This a seven man squad with five storm bolters - 20 shots in rapid fire range wounding on 2+ due to Hellfire rounds via Special Issue Ammo (SIA). Use Mission Tactic to reroll 1s to wound. Watch Captains or a Watch Master grants the buff aura to reroll missed hits... that’s a lot of wounds no matter how you roll it.
The Black Shield allows the squad to heroically intervene and they have a lot of attacks for melee making them an excellent counter punch unit. It’s all about good placement using a good screen such as Space Scouts from another detachment. The Terminator has two base wounds along with the 2+ armor save plus the 5++ invulnerable save, helping the squad to efficiently tank wounds along with the two storm shields. The Infernus Heavy Bolter provides longer range dakka and can use the Hellfire strategem to inflict d3 mortal wounds. Couple the flamer with the frag cannon as an anti melee deterrent when on overwatch. You can also sneak in the Tempest Shell strategem for d3 more mortal wounds. This squad is super killy and can deep strike to protect against an enemy alpha strike.