So, first, some things that haven't changed: there are still four Domains, and they're still the ones you know. They also still contain the same Spheres as subordinate stats (much like Talents are subordinate to Aspects), as you can see in this handy reminder table:
|Celestial||Heavens, Solar, Lunar|
|Devotional||Divinity, Ritual, Theology|
|Elemental||Fire, Thunder, Water|
|Spiritual||Death, Fortune, Life|
But what did change, and how are you going to purchase and use Domains and Spheres for your Heroes now?
First of all, our initial conception of Spheres was very freeform, and it has since solidified. In the original version, you did not purchase dots of Spheres; Spheres were just organizational concepts inside Domains, navigated via webs of connected bonuses and Blessings.
You still do use the web above to get around inside a Sphere, so no worries there! However, you will now purchase dots of Spheres within Domains, and how many dots you have in a Sphere will matter to gameplay regardless of where you decide to go as far as nodes in the tree are concerned.
We did this for a couple of reasons, and they're all good, crunchy, mathematical ones, for those of you who are big fans of us doing things Because Logic. For one thing, it's more symmetrical and makes more sense when stacked up against Aspects and Talents; now, essentially, Aspects and Domains function the same way as container stats for Talents and Spheres, which have their own dot ratings and affect rolls. And for a second and much more important thing, at least as far as balance goes, we needed Domains and Spheres to have their own in-house way of handling rolls for activating Blessings, and that means that Spheres needed to have a functional use beyond just looking pretty.
So what do you roll for Blessings? Well, that depends on the Blessing and what it's designed to do. Previously, we had said that Blessings from Domains would roll using the Aspects and Talents; that way, your other hard-won skills could be involved in your use of Domain powers, and we'd be able to do neat stuff with making each power roll Aspects that were appropriate to its function. However, we found in testing (and some concerns aired by you folks, too) that this made some Spheres "better" than others for some character builds, and that it was easier to game the system by choosing certain combinations and not having to perform much investment in both, leading to potential situations where all Warriors are also Elementalists or all Sages are also Spiritualists. We didn't want to make any of the Domains feel "mandatory" for any character build, nor "useless" for any other, so we went to the simplest solution: you now have to also purchase Sphere dots to make things work, thus preventing players from buying a single dot in a Domain, getting all the bananas powers in it, and getting to lay waste with them without ever buying any stats they didn't already have.
So, like Talents, Spheres now provide automatic successes to rolls, in order to complement the dice granted by Aspects/Domains. However, we did still like the flavor and flexibility of being able to have Aspects involved in some Blessings, so we didn't completely boot that concept out the window, either. Now, there are two possibilities for what you might end up rolling to use a Domain Blessing:
1) Domain + Sphere (so, for example, Elemental + Thunder or Celestial + Solar). This roll turns up most often for Blessings that feel like pure expressions of a Sphere; a Lunar Blessing that has to do with embodying the moon or shedding pure moonlight is likely to make this roll, as opposed to one that might have more practical application or affect things other than the Hero's mooniness at that time.
2) Aspect + Sphere (so, for example, Hunter + Life or Sage + Fortune). This roll happens when a Blessing involves using a Spheres powers to do things that might normally fall within the purview of one of the Aspects. For example, powers having to do with divination or predicting the whims of fate might use that Sage + Fortune roll, since finding information is normally first and foremost the Sage's job, or breathing fire on someone to attack them might use a Warrior + Fire roll, since you're obviously being a warrior and taking the fight to your enemies.
We did discuss the elusive Domain + Talent combo (Celestial + Mysticism, or something like that), but after a lot of testing and investigation, it turned out not to have a lot of uses, and to be awkward and balance-problematic, so it's been sent back out into the cold for the time being. It might make reappearances in future expansions, although we won't promise anything.
So now, with this change, you can build more flexible and capable characters, depending on what you want to do. Heroes who want to purchase Domains and Spheres to complement what they're doing in Aspects and Talents can, without fear of accidentally setting themselves up in non-viable character builds or feeling the pressure of being "required" to take the Domains that are mathematically best for their Aspect regardless of what they want to do. Heroes who invest heavily in Domains and Spheres are rewarded by having some powers that they're complete dynamite at, and others that, even if they aren't as good as someone who had the Sphere AND the Aspect being rolled, they're still pretty great at by virtue of their great powers over Death. There is definitely a little more XP investment, which we recognize is annoying when you want all your great powers right now, but we think that's more than made up for by the resulting flexibility and possibilities when it comes to building different kinds of characters.
Okay, so there is also a little tiny flavor reason for this change, which is that it also makes more sense for various heroes and deities to have to specialize into Spheres instead of wandering around them all willy-nilly. Most Heroes are famous for, say, using a lot of Fire, not for using a lot of Fire/Water/Thunder/Earth/you know what, whatever element comes to mind. There are a few out there, but most need to focus down (which is why those few are interesting as characters; the Avatar wouldn't be all that special and interesting if everybody else in the same world could also wield all four elements instead of just one!).