Sombra is going to shake up the meta pretty hard. She's basically a counter to the top three hero picks in comp (Zarya, Rein, Lucio) and herself soft countered by heroes with lower pick rates (Winston, Soldier, Hanzo, Widowmaker). The way she counters Lucio though is borderline cruel, heh. "Let's break it dooown!" Nope. "Lights out!" Canceled.
She is immensely fun to play though, just from her mobility. I've only been able to play her in custom games with bots so far... Arcade is basically 6v6 Sombra atm which is kinda dumb, and the other modes with 1 hero limits, people just leave the game if they can't pick Sombra. Looking forward to seeing how she actually performs with and against real players.
[Edit] Apparently Soldier is not necessarily a counter to Sombra, as his tactical visor doesn't track an invisible Sombra. Thought Tim Ford (OW Dev) mentioned that it would track her during Stylosa's Blizzcon stream, so I guess I was wrong.