The lore does support Deathwatch heading out en mass to deal with a threat that a small team could not. The heart of the army (and the only troop choice) is the Veteran squad. Talk about options. Anybody can take any ranged, melee, or special weapon. Plus up to four heavy weapons. Yikes.
Of course this will make the squads get real expensive real fast. Especially if you add the new fancy Corvus Blackstar Dropships as a transport. Which I will.
Terminators, Vanguard Vets, and Bikers (no attack bikes) round out the infantry types. All of those squads are limited to five models. Regular and Venerable Dreadnoughts are available as Elites. All three types of Land Raiders make up the only heavy choices. Some really unique wargear are available, such as the amazing Deathwatch Frag Cannon, Heavy Thunder Hammer, and Infernus Heavy Bolter. And so many different formations.
Death to the Xenos
Not Just the Ugly Ones. All of Them.