This is a great substitute for Marked for Death.
The cloud deals 34% weapon damage per second, and every hit and crit counts towards both Night Stalker and Shadow Power's life steal.
Shuriken Cloud doesn't require Shadow Power to be active at all times to get the life steal benefit (and I'm sure if this applies, you also don't need Caltrops to be laid down at all times to receive the crit chance benefit). What you can do with this is cast Spike Trap and Shadow Power BEFORE you apply the shuriken buff, and you get the full benefit of all of this for a total of 120 seconds.
I'm getting 60k crits with this buff active, and the life steal effect can sustain my health pool through almost all damage.
Anyways, try it out... and I hope they don't nerf this.