Casting traditions are indeed restrictions on a characters casting abilities. They are a set of drawbacks and boons (boons are purchased with drawbacks) and any drawbacks that do not get used for purchasing boons will increase the characters spell points.
The 3 normal casting traditions found in pathfinder are included as options in SoP. Traditional magic is Arcane, Divine Petitioner is divine magic, and they also have druidic magic as option.
You can also create very different methods of casting like Runic casters that have to use Profession: Calligraphy to successfully cast their spells, causing spells they cast to take more time. Or Blood magic users who take damage whenever they use spell points but have many boons that increase their caster level under certain conditions. You can even make characters like in the Avatar: The Last Airbender cartoon who use martial forms to control and direct elemental magic.
As for the destruction sphere, the increase to a D6 for force is a recent change and we are testing it. Keep in mind though that each of the different elemental blast options have their advantages even when they do not increase base damage. Fire leaves creatures burning, lightning gets a hit bonus against those wearing metal, stone ignores antimagic fields and spell resistance etc. Plus, having options in the damage you deal is helpful because while it is true almost no enemy has resistance to force there are also almost no enemies that are weak to it.
* I just noticed that Drop dead studios answered these but I went through the effort to type it out so I will respond anyway :-)
1: no, Spheres of Power caster levels are considered part of a their own seperate system so they do not stack with normal pathfinder caster levels.
2: the system is made so that it can work in the same world as traditional vancian magic. there is even a prestige class that combines the two. It also works as a replacement of course so it would be up to the DM.
3: I doubt this will be answered as I honestly do not think even the designer can be sure of this.
4: If it is the first SoP casting class you have gained you gain the number of talents listed for 1st level + 2 more. Each talent can be used to gain access to a new sphere or one of the talents in a sphere you already have access to.
5: There are not very many of us who are active in the message boards so this is hard to say. one play group said they encountered some balance issues and that SoP was stronger than it should be. However, I think this mostly came down to the way the DM played things and was not due to the system itself. We also just got an updated version of the system that likely solved the issues we had previously found. Over all, I think it is very balanced but any system that lets you pick and choose effects like this does is likely to get a bit unbalanced if you give your players 100% free reign.
6: They do. All companions you have advance according to the chart. remember though that do not heal until you rest and regain spell points.
7: You would need to spend a spell point to maintain any more than one summon. if you had the easy focus boon you could maintain up to 2.
8: concentration works the same as in pathfinder. there is a boon (easy focus) however that lets you maintain concentration as a move action however.
9: All SoP classes choose casting traditions. They are built into the system. The GM needs to decide what casting traditions they will allow in their game.
I can't give an official answer of course but judging from the current progress I would say the chances of this releasing before christmas are very slim.
technically you can let your players create your own casting traditions. However, like any system that lets people choose their advantages and disadvantages this has the potential to be taken advantage of. If everyone in your gaming group are equally savvy at powergaming and the GM is prepared this probably won't be a problem.
I also think spellcrafting sounds cool and I look forward to learning more about it. I actually am really looking forward to learning more about all the advanced magic.
The system is indeed still being developed. The biggest problem right now has been that of the two or three people originally working on this project, only one is still on the project as the others either got higher paying jobs or had long term family emergencies and had to leave the project.
Despite that bad news, things are looking very good for the project now. First I will answer your questions directly then I will add some extra info that I believe should be allowed for me to post :-)
Is they system fun and/or easy to use?:
Are the classes balanced with current caster classes:
Now for some info:
Caster level in Spheres of Power (SoP) is treated somewhat like BAB. Different classes gain caster levels at different rates. There are 3 "tiers" of casters; low, medium, and high. Low casters gain a caster level every 2 class levels. Medium casters gain a total of 3 caster levels for every 4 class levels. High casters gain 1 caster level per class level.
There are 20 spheres in total. Each sphere has one or two basic abilities and ~7-28 talents that can be chosen. Talents either modify the basic abilities of a sphere or give you new options. Some sphere abilities can be used without using spell points and some require 1-2 spell points.
There also Advanced Talents for most of the spheres. These talents have prerequisites to acquire and tend to be more powerful than normal talents. They also tend to have effects that have major effects on campaigns and are therefore only allowed if the DM says they are and are not part of the base system.
You can also create your own Casting Traditions (think arcane magic vs divine magic). They have 9 casting traditions already made up and give you the ability to create your own casting traditions by using combinations of the 26 drawbacks (14 of the being sphere specific) and 6 boons. This is mainly a DM tool but if you are brave or trust your players to not min/max to much you might let them make their own traditions.
There are several things that we do not yet have any testing information on yet. These are:
-Rituals: these are supposed to be somewhat similar to traditional spells but they take a fair amount of time and resources to use.
-Spellcrafting: this will allow people to combine talents from multiples spheres into a single effect.
-Incantations: used by the dm to allow customized effects that can be used regardless of class or level.
All of the above is, of course, subject to change but I hope you have a better idea of where the system currently stands :-)