The main thing about engineering is AoE and survivability. You'd wonder what makes engineering so resilient, it's the Tier 6 skill, deployed shields which basically transforms you into a heavy armor class when you take cover. The other thing is more powerful shield probe. I still have no idea how much damage that thing can abbsorv but it's huge with engineering. And since you have EMP Detonate, you can get a second one shield probe when the first one ends.
In combination with ballistic dampers and entrench, this allows for some pretty good burst damage mitigation.
As engineer when you are fully min maxed for power (PvP) your probes absorb close to 4k. Highest single heal i have ever had is 3.7k coming from shield probe. Naturally, since you can pop that baby twice in a fight, you become very tank like. In duels you can fight anybody except DoT specced classes who know how to kite and how a pillar close by
I have played all 3 sniper specs and I like all of em, but when ever I go PvP, rated or just full premade for normals, i always spec engineering, since i so miss the survivability and extra stun. Somehow followthrough and 30% higher crits from marksman tree seems less important to me.