I think the idea of health as a resource is really cool and different gameplay but the current iteration of Blood Ritual looks broken to me. See if I'm missing anything here in the maths:
15% of Mana costs are paid with Life. In addition, you regenerate 1% of your maximum Life per second.
The most extreme mana rotation I can think of is spamming Locust Swarm (196 mana) with a 1.5 speed weapon under the effect of Big Bad Voodoo, which takes 353 mana/sec (give or take). 15% of this 53 life/second.
53 life is 1% of 5300 max life.
So for a WD with more than 5300 life it's impossible to lose life through blood ritual. From all the predictions of high level life numbers, most WDs will pass this threshold well before 60.
It's a bit disappointing that rather than new gameplay, Blood Ritual turns out to be just a flat mana cost reduction and a small HoT. I vaguely recall times back early in the Beta when life pools were much smaller, mana pools much bigger and Blood Ritual was 50%. That seemed like a cool skill, but like many others it's been nerfed to nothing.