Symmetra wields a beam weapon that does more damage the longer it's attached to an enemy. She can also fire out slow but powerful balls of energy. Those turrets can slow enemies, and she can also buff allies with a shield that reduces damage. Her ultimate is a teleporter.
Rumors say that Symmetra's weapon looks less immediate and satisfying than those of previous characters. She's clearly quite mobile, though, which is a key difference between her and the Engineer, in his default loadout at least.
Overwatch's beta is due to start this autumn.