I agree, Syndra still needs some love.
I re-watched her champion spotlight and it said in team fights you should disrupt the battle.
But how? Her stun can hit several champs, but that leaves her vulnerable (Except for flash) aand the stun only lasts 1.5 seconds. With a bit of tenacity, its barely noticed.
Same with her slow, its very weak.
I say, let her Dark Spheres grant vision (For like a second as they form) and have them slow the targets, which will decay quickly. They also need to last longer.
Her W should last longer, and the grabbed sphere/minion should be held closer to her, so it can get to its target faster. Also, its slow should be increased a little more than 33% at Rank 5.
Her E is fine I'd say.
Her Ult should have some additional effect, like crippling the enemy (Reducing heal and slowing them... they were hit by "cataclysmic power" after all.) because nothing is worse than ulting an enemy and watching them escape with 50 hp left!
Also, her PASSIVE. Give it some additional effect, and let it also benefit Unleashed Power at Rank 3.
For an additional effect, why not increase her base attack damage by #% of her AP or something?