I've found Shadow self heals to be superb through the use of Devouring Plague. But mind you, this is only in combat. Not something you can do to heal up after a fight.
But so far I've found Shadow to be pretty great. Bubble on CD (short now with the talent+perk) and devouring plague is really all I need to stay alive. Dev plague is up so often thanks to Mind Blast having a 3 sec CD and being instant cast thanks to Clarity of Power (best 100 talent by far).
But yes, I agree flash heal is a joke. Replace it with a shadow version of renew and either buff or completely refine Vampiric Embrace because it's disappointing how long it's been in it's heinous state. I don't want the old VE back really because I hate having to keep heal flytext turned off.
I'd like VE to be something like this: 5% all single target damage passively heals the Priest. On CD, buff this to 15% and allow it to heal the entire raid for a short period of time.