Crystal Shard in Dark Magic is a fantastic ability. It will kill weak mobs with two hits and it has a 2 second knockdown. I have a pet too but mostly just to finish off the mobs after hitting them with Crystal Shard. To be honest I haven't found anything else in the lower levels that's really worthwhile for me, so I've ended up putting points into crafting skills. Although, I think Rune Prison for crowd control and Bound Armor for durability may help out in later levels.
Yup, that crystal ability is great, also the familiar is worth getting just so it can tank some damage when you pull mobs, you can also morph it so that it explodes when it dies for that extra bit of AoE damage, combine that with the ability that gives you magicka back when a familiar dies and it's quite handy.
I use the crystal shard and the lightning spell, paired up with a bow and some medium and light armor, and I'm able to stand my own. Of course, I haven't put a single point into my health and just been stacking magicka.
I have a storm caller build presently... I start with an elemental wall that explodes... followed by an 8 second storm armor, and auto attacks. I use the instant on enemies that are low health to explode them (I have it morphed to restore mana).
And the stormcaller ultimate is just awesome. It's a good aoe build!
I can usually take on 3 or 4 mobs at a time. Probably more if I could just level up my tailoring faster...
I haven't got very far on my sorc yet, and I'm leaning towards a heal focused build, but I'm finding daedric curse quite satisfying paired with shards for a burst damage/ CC combo wombo. Plus it just sounds awesome when it explodes. It reminds me of burst damage sorcs in Warhammer, if anyone ever played that.
I think it will be useful for pvp and solo or kiting situations, and not so much for grouping where things die extremely fast, as it takes a bit of time to do damage. But hey, I'm low level, so it's quite possible my opinions on this could change.
My sorcerrer is a Kahjiit with medium Armor, a bow, and dark magic--works very well, though I have yet to take it to pvp and see how it does, but I have been able to hold my own in pve. I put points into magicka and stamina, with skill points in poison arrow, evasion, crystal shard, encase, rune prison, and negate magic, as well as magelight and a bunch of passives to boost stamina and magic regeneration, while my armor is mostly enchanted for health or damage increases. I also put points into the Kahjiit racial abilities except for carnage because I have yet to use a melee weapon, though I just hit lvl 15 and am contemplating making the second weapon a restoration staff, or dual wield, in which case carnage might come in handy...