Terran's Hard Counters: The Thor and Marauder
From what I've seen from accumulated video streams, is that Terran can mass these two units in very basic ratios which hinders balance and counter measures for the other two races; Protoss and Zerg have to take desperate maneuvers (unit combos) in order to deal with them.
This is a problem. Marauders have managed to become SC2's Dragoon unit. Capable of being massed at efficient levels due to its simplistic counter-role. Fortunately, it is only a Ground-to-Ground fighter which may balance out this subject.
The Thor is a bigger problem. I've always believed, since being revealed, that a unit like the Thor or the Protoss Mothership should be a unit of rarity. It looks like a power unit too expensive to be made in max production, but powerful enough that you'd be foolish not to have at least one in your unit combination. Blizzard needs to find a way to achieve this.
I was amazed at the new GStar videos on how easily the Hellion and Thor combination was effective against a number of different unit combos vs. protoss and zerg. It looks like the Tank/Vulture combo all over again. Except now the Tank has a profound Anti-air role and the Hellion is just as good as the vulture.
The Thor's attributes need to be nerfed, or its role needs to be downplayed so that it doesnt become a unit worth of mass production. The thor looks like it would be accompanied by a tag-team of marauders, marines and tanks. The combination of just Hellion and Thors is way too easy in terms of racial challenge of dealing with certain threats and in terms of specific race counters.
Zerg's Weakness: Tragedy at Tier 2
The problem I believe worth mentioning is that Zerg tech. units end up being a re imagination of linear SC1 concepts. While Terran gets a huge overhaul in many sectors of SC2's gameplay, the Zerg are still stuck with spell binding actions to deliver blows against the enemy.
I feel the Zerg need a unit capable of scaling cliffs or something to redefine the way the Zerg travel. I've said this a few times before, but the Zergling could use a new upgade - an upgrade that could allow it to scale cliffs (perhaps the use of those wings found in the earlier Zergling models would suffice as far as the lore goes).
The Nydus Canal is along the lines of that notion but it ends up being a side-project as far as being an offensive strategy - there are other efficient ways to deal with threats.
I want to throw this idea out there:
Why not make the Corruptor make the child unit of the Overlord? Have the Overlord evolve into the Corruptor instead of the Overseer. Perhaps give the Corruptor some of the attributes the Overlord/Overseer has in order to balance the changes in strategy transitions. This ways, also, the Zerg have a Tier 2 option that could mend the supposed problem Zerg has been having (it is said that it is the weakest race atm).
Protoss: A simple combination of many
The protoss seem to have the most varied of attack options. They have plenty of interchangeable unit roles and counters which I believe Blizzard is forgetting to use as a reference. Now I understand that each race needs to be different but the Zerg could pick up on a thing or to that is displayed by the Protoss. They are well-rounded and have a vast dimension of depth as far as available counter measures. The Protoss seem to need a variety of units to deal with threats but it isn't a strict ratio of units to do so.
This is different. The Zerg seem to require a larger amount of variety and inexplainable ratio numbers to deal with its threats. This needs to be adjusted in order to gain ground with SC2's fans. I would give a suggestion to help solve this but I don't have one
Back to the Protoss; The Immortal seems dead in the water. Has anyone seen this unit in action yet? I personally love this new unit but it needs to be catered to and atm, there arent a lot of useful counters on my wishlist.