I find it curious that SC2 and its predecessor, BW, are so dramatically different. There are numerous balance/complain/bitch/whine/moan/etc threads on SC2 and a handful of people saying to give SC2 more time/bw was a fluke/etc.
The discussion of balance in SC2 has been discussed to death, and I have stayed silent because no one listens to what everyone else has to say. As my math teacher once said, "If god believed that speaking was more important than listening, he would've given us two mouths instead of two ears." What ends up happening is people are giving balance proposals and complaints with no real reason at all.
Hopefully, my wall of text will put an end to these balancing threads...
Allow me to start with a control group and a basic subject. Since most of us are familiar with BW, let's compare the units of SC2 to BW. Picture each race as individual communities, with the unit compositions as populations and units as species.
Looking at the units in BW, a few general trends we can see in most units are that the designs are simple, flawed, and unique. The zealot is a simple, unique melee unit that is limited by the surface area of the opponent's army. The siege tank is a long range artillery unit that is limited by how well it is protected. The mutalisk is an an all-purpose air unit that is limited by how strong the opponent's anti-air is.
12 years of natural selection have passed, weeding out the successful from the useless (i.e. the scout). Perfect build orders, perfect unit compositions, and victories dependent on skill and execution became the "identity" of BW.
If we look at nature, the most successful species are the ones that coevolve with one another, work around their flaws, and have a simple feature that distinguishes them from the rest of the animal kingdom. Roaches are known for their vitality and numbers. Birds have wings and unique physiology. Humans have thumbs and a big brain.
Lets take a look at the units in SC2. In comparison, half of the units have a far-fetched concept, no real weakness, and they aren't unique. The thor shares a niche with the siege tank. The reaper is a flying marine. The roach and the hydralisk practically share the same niche as well. The immortal is just a beefy stalker.
What it looks like, in my opinion at least, is that Blizzard took the successful units from BW and eliminated all of their flaws and enhanced their strengths. The flaw of the siege tank was it's dps and rate of fire. Hydras now do normal damage instead of explosive damage. Goliaths got a 275 hp buff, +47 ground damage, and a nerf (or a buff, depending on how you look at it) in anti-air... The list goes on.
Now the real problem occurs. If you picture each race as an communities, the species in that community will naturally undergo evolution; one aspect of evolution is natural selection. The best will survive to be used again while the weak will fill a lesser role.
This wasn't a problem in BW because the units had their strengths and weaknesses.
This is a major problem in SC2, where the flaws have been covered up and new flaws have been randomly added in.
Blizzard broke a key fundamental rule in evolutionary science; organisms do not evolve instantaneously -- species adapt overtime to fit into the environment.
What we have now are a conglomeration of units that will not work together at all.
You can't just say "oh, since moths get eaten by bats, lets replace them with a moth that has super speed and super hearing, and now since the bat can't catch the moth, lets make a special bat that shoots acid so they can catch the moths."
You can't say "oh bears are omnivores, so lets stick them in the middle of Africa."
Moths and bats coevolve; they don't magically gain traits they never had in their gene pool. Bears aren't going to migrate 10,000 miles to go to Africa; they like their niche in where they are right now.
Likewise, you can't randomly stick the Thor in the middle of the terran arsenal and expect us to seriously use the siege tank. You can't give the zealot a super buff and give the terrans a super counter.
If Blizzard messed with the natural selection of individual species in SC2, the populations of unit compositions will be even more messed up. Let me sum it up for you:
A race dependent on it's variety of specialist species. The generalists in the Terran arsenal are easily wiped out by the other races, which incline terran players to quickly end the game before the other races can wipe out the marines, marauders, and hellions that are crucial to winning every game. With no generalists, the specialists are vulnerable to anything outside of their optimum zone.
The best refined race in SC2 right now by far. It is dependent on how well the population of units are suited towards the given situation. What ends up happening is that the situation is created by the army (4gate stuff) or the army adapts to the situation (fast obs builds). The weakness of toss is in it's lack of units that can maintain map control, which encourages 1 base play and makes 2 base play rather difficult.
A race made entirely up of generalists. Ling/Bling/Muta can be used effectively in all three matchups, but they lack enough specialists to deal with certain army compositions like mass thors. The lack of diversity with zerg makes it extremely predictable, which encourages the other races to stick to 1 base harassment builds. The strength of the mid game zerg army is also extremely formidable, which further encourages 1 base play.
Seeing a common trend here? The way SC2 was created is flawed; the individual units are balanced but the distribution of specialist and generalist units are skewed. As a result, games are basically competitions between species and populations of units -- not the actual race itself.
Blizzard can take away chat rooms, LAN connection, and put in retarded achievements, but you cannot fuck with mother nature. Right now, we have exotic species in an ecosystem which is a recipe for disaster. But with future expansions and patches creating a new ecosystem ahead, I have faith that Blizzard will create a new environment and create units to fit into it.