Shadowmagic
Well, as my backup character I made our first mage, and realized it would definitely play much differently than other characters. Some parts of it look ridiculously overpowered, but others look like you end up with less overall diversity because it costs so much in both build points, credits, and karma.
For example, his basic spell, Stunbolt, will likely incapacitate any metahuman other than a troll in one shot. One silent, invisible shot, where I don't even have to act like I am casting a spell. I get 11 dice vs. the opponents Willpower only, likely 2-4, with a base damage of 6s. On average I will get 4 hits to my opponents, 1, doing 9 damage. So maybe not a 1 shot kill, but it might as well be. I can also overpower the spell to up 8 easy enough. (all spells can be overpowered up to twice their force, so I could do a Force 12 Stunbolt; increasing the force makes it more likely a mage will take damage every time they cast a spell)
On the other side of the coin, the Mage version of cyber/biotech is both very expensive and costs karma, where most characters don't lose anything adding most tech (well, other than essence). For example, a talisman to add 3 dice to one spellcasting category would run 45,000 credits as well as 12 karma. The additional possibility of losing the item makes it very scary; high price is one thing, but losing 12 karma because someone steals a random item from you would be very discouraging.
Also, Drain is another balancer to mages. Every time a mage casts a spell, there is a chance he takes damage; the more powerful the spell, the more damage he can take.
Summoning spirits also seems pretty powerful (though this is also the easiest way to knock yourself unconscious). A basic Force 4 air spirit has 16 reaction, Dodge 4, plus Immunity to Normal Weapons giving it Armor 8 (however, if the DV does not exceed 8, the spirit doesn't even have to roll a damage resistence test). At that level it probably won't do much damage, but is nearly impossible to kill. A Force 6 spirit is up to 24 reaction, 6 dodge, and armor 12 and could do a lot of damage (6p).
It will certainly be interesting to play. It might make parts of a particular adventure very easy (combat mostly) unless spellcasters regularly show up as NPC's. However, that could add even more to the easy lethality of the game.