Deathtrigger is the classic combination of Gunslinger, Archery and Shadowplay - two ranged skillset along with a DPS-oriented Shadowplay skillset that also provides much needed utility.
The Gunslinger and Archery skillsets provide an immense amount of damage and hence we spend most of our skill points in those trees. It provides us many skill rotations that we can use to burst down opponents. The passives from both these skill trees are focused on Ranged damage, which is exactly what we want as a Gunslinger class. More importantly, it gives us more skills that go PEW PEW, and who doesn't like more PEW PEW!
Shadowplay adds in much needed support skills such as Freerunner and Pin Down, as well as utility in the form of Drop Back and Stealth. This complements with our burst-oriented approach of the class.
One of my favorite combo present in this class is Room Sweeper -> Stealth -> Recurve -> Concussive Arrow for a MASSIVE amount of burst damage that can often one-shot an enemy!
Deathtrigger is nothing fancy, it is just a solid class that is naturally synergistic. The power of the class is in its flexibility and effectiveness over anything else.