I've very much come to enjoy this particular approach to Malthael after his rework:

The key talents for this build is throwing shade (which, with the mana cost cut you can spam at your own free will), and final curtain - which makes your deathshroud linger for 4 seconds. This allows you to mark entire objectives, block paths for the opponent team, what not. The rest of the build helps you play from a distance and escape when you need to.

The main idea is to only engage in close quarters when you are about to seal a kill. So keep your distance, poke with shroud, slow/heal/damage with soul rip. Then, when it's almost over, wraith strike in, last rites, and send them to forever after.