For the moment, the "OP" units (though not game breaking) seem to be the Hellbats and the Tempest. I really feel that it's because they are new and people haven't found a good way to fight them yet (for the same reason voidray collossus was "OP" until zerg found out about fungal growth).
Starcraft 2 is made to be a competitive game, so all races have to be able to play against all races. Blizzard wants most unit in each race arsenal to have a role in most matchups. That is why the changed the reapers in HoTS, that is why the hydras got buffed and that is why the voidrays got changed too.
tldr; no, nothing is game breaking otherwise sc2 would be boring. Blizzard said the mathchups win/loss were pretty close in pro matches in a statement last week about game balance. They know about skytoss but they want to wait before doing any changes.
EDIT: I saw in the comments of the question that sources were asked, so i started doing some ressearch to help with my claims.
Charts of the win/loss:
Intwerview with Dustin Browder by Frodan: http://www.teamliquid.net/forum/viewmessage.php?topic_id=382616
IAMA with blizz dev team: http://us.battle.net/sc2/en/blog/8983614/Reddit_AMA_Full_Transcript-3_6_2013
balance report just before HoTS release: http://us.battle.net/sc2/en/blog/8896362/Situation_Report_Heart_of_the_Swarm_Balance-3_4_2013
These are the stats I could find for now.
The race distribution is in WoL because Sc2 ranks have not updated their database with enough HoTS players for it to be reliable for now. Like it has been said in the comments, the balance of the races is a lot about skills (which is why it is so hard to do a perfect balance).
When you lose a game, check the replay, how many workers did you have, what were your upgrades, what was the angle of attack, did your opponent hide expos or tech, etc.