Queen - can't be used offensively, gives early AA to the Zerg, which is nice. Able to heal hatcheries, also nice, able to spawn extra larva, which is awesome. Not really OP because she's incapable of attacking
Siege Tanks - lol, this things are so awesome for defending bases. You almost can't attack Terran in the middle game, you become the reactionary force. You can also fly factories and place them on cliffs near the enemy base. They can't see you without spotters. This is almost imba unless you have cloaked air scouts.
Terran have amazing capability to expand with flying command centers.
Stalkers are very strong if you can micro them well. Every time one runs low on health you can blink to the back lines. If you're chasing you can blink on top of them and finish them off. If you're losing you can blink away. They're probably the best units for the terran.
The new Terran air units are pretty awesome. You can send seeking missles that have splash damage at enemies. Burrowing does not dodge them either.
A large force of roaches is very, very strong, but is beatable.
Medivacs are an awesome counter to stalkers. If you (are korean) have really good micro, you can put your units in the medivac and then drop them quickly to DODGE THE ATTACKS. This isn't new however, it was in SCI.
The air units are really good if you can't counter them. If you build an army of zerglings and encounter an air army, you're totally effed. Medivacs, warp prisms, and other transport air units are awesome for harassing.
Helions are crazy fast, so they can be micro'd out of enemy attacks while firing. They can also just blow past your army and into your base to pound on your workers.
I'm surprised no one's complained about thors yet. They're crazy good for their cost. (I'm guessing most games don't last long enough for thors to get out on the field)
Right now, I'd say terran are the most powerful, but overall it's pretty balanced. Teching has become a lot more important than ever before. Low tier units cannot win (save a quick zerg rush with good micro against a bad player)
The new protoss unit that creates impenetrable force fields is SO CHEAP. You can attack enemy workers, plop up some shields between buildings, and kill them all before the force fields wear down. You can lure the enemy army into a choke point, put shields in front of them and behind them so they can't move, and then beat them down with ranged fire. You can always escape with a force field. You can block entrances to your base with force fields. You can block enemy escapes with force fields. YOU CAN DO ANYTHING WITH FORCE FIELDS!
Sorry for the long, rambling post, I just jotted down my thoughts in no real order. 
