While I am not a fan of Deathwatch due to absolutely loathing Spees Mahrins, the concept can be interesting if you want character to your numbers. It's quite a challenge to describe your character, since you've got certain frames to work within, and armor too. The personalities withing the group will vary quite alot aswell, and having different cultures withing the space marines chapters makes for interesting moments aswell.
But yes, the Deathwatch adventures tend to have quite a focus on murdering things. Because of some reason or other.