Yeah, I'm not going for full glass cannon but I'm still weak to survive high torments. T1 at least is as easy as it gets. This build works great for single targets like bosses, but with vengeance, it just crushes everything in its sights. Here is the build:
While I'm using passives that help me to survive (Awereness is awesome) and you can go full DPS if you want, removing Preparation, Perfectionist and Awareness. However, I do enough missile damage to clean out mobs fast, elites even faster using vengeance and rapid fire. Vengeance + Rapid Fire + Mortal Enemy in bosses is awesome (And you can go for single out instead of any defensive passive in bosses).
This is my toon- i farm quite nicely T3 and usually we go rift in t3 or t4 depending if we have a "tank" available or how fast we mow through mobs.
In game i have something around 370k HP and less than 7 million toughness; i find Awareness pretty bad since from dexterity i have already 40%+ dodge which is only going to get higher with better gear - but if you have troubles with survivability, it's a decent option.
Only thing i must say, it's Rapid Fire. It does nice damage, but it keeps you standing still and movement is a high penalty due to its activation cost (btw, only skill in game to have that -.-). If you plan to go higher difficulties, you're going to move a lot making RF more a chore than else.