Yes, it's a decent talent. No, it's not something I think is more powerful than the alternatives. You figure out a spec that retains CoH, 6/6 IHC, 3/3 Serendipity, 5/5 Holy Spec, and 2/2 SoL while obviously keeping Meditation that also manages to get 2/2 Holy Reach, and I'll talk.
Drop desperate prayer and get 1/2 divine reach. My experience is that people simply don't realise what divine reach does for CoH. Its not easy to spot the fact that you are missing a target every 5-10 CoH, but if you do (and there are very few enounters where you dont) its easily a drop of 2-5% healing. Everytime you don't use CoH because you are missing 1-2 targets every time you cast it, divine reach is worth gold.
There is no question that divine reach is better than desperate prayer in terms of healing output and efficiency. Desperate prayer only pays its divident everytime it saves your life.
This is what I will spec at 80: Talent Calculator - World of Warcraft
@lvl 70: SoL+CoH -->20% crit:
chance to proc SoL = 1-(1-0.20/2)^5 = 0.40951
@80: SoL + CoH --> 25% crit:
chance to proc SoL = 1-(1-0.25/2)^6 = 0.551204681
Obviously you will get a lot of procs, but what does each of them do. Each proc gives you a free flash heal, but this FH cannot crit, and cannot proc serendipity. So that means the mana value of the heal is the mana cost of an FH, minus the FH glyph, - serendipity return - clearcasting.
At 70 with say an average serendipity return of 80%, 20% crit, and the flash heal glyph, that means 360odd mana. With 20% crit chance you also get 6-9% clearcasting which further reduces cost to ~330 mana. To give SoL every benefit of doubt I am going to ignore the fact that a clearcast has a better return than just reducing cost.
At 80 rasing the crit to 25% each proc saves you ~500 mana.
At the very best of situations u can use an SoL every 5 seconds. That means 330mp5 at 70 and 500mp5 at 80, or 165/250mp5 per point.
It certainly looks like a lot of regen, especially considering that healing prayers returns 35mp5/48mp5 or so from PoM and maybe something similar from PoH if you use it.
This is the theory anyway and it paints a far rosier picture for SoL than it deserves. In practice getting 1 SoL flash off every 5 seconds, is very very tough indeed. In BT I barely got off 1 every 15 seconds, despite heavy CoH usage, simply because it was pointless to use it. In most cases the damage would get healed by the AoE healing anyway, so the SoL just wasted time.
I personally dont accept that SoL is worth anything more than 80mp5 per point at 70 (I can't say much about it at 80). Its still more than healing prayers, but healing prayers doesn't make me bleed HPS.
I consider this a classic case of ppl getting excited about a talent that is not actually that great, simply because it procs a lot.
Comparing lightwell with SoL, it would take 15 SoL procs to produce the same healing and I just can't see how its possible to get that in under 2 minutes. However 15 SoL procs also cost you 22.5 seconds of casting time, while the lightwell just costs you 1.5 seconds. My personal experience is that that even if only half the charges of lightwell are used, it has a better return than SoL.
SoL is not a musthave at all. It can have a decent mana return, but its not really any better than the alternatives. Its a great deal of micromanagement, for no good reason. Lightwell and healing prayers, not only give you overall the same return, they also take a lot less micromanagement on your part and make PoH more usable opening up another option. Less time monitoring procs = more time concentrating on what you have to do.
If Divine providence is also changed to reduce PoM cooldown, then healing prayers will be hands down better than SoL.