The Zerg easily the most feared at this point, being able to out produce both races at workers, and can easily build military units faster than the other race. Though it's nearly impossible to stop a cheap zergling rush on a small map, it will put a zerg at a terrible economic hole if it's unsuccessful. The Zerg also are given a free scout and detector in beginning of the game.
So finding the other players is easy. However with the respawning of the larvae slowed down, there is need for more hatcheries which are cheaper, turning the Zerg into a very defensive race in the beginning, almost forcing you to build sunkens. Sunkens are also very cheap, and do a very good job against any early attack. The Zerg's only problem is that they must play defensive early on since it's very hard to maintain an offense with 1 hatchery.
When the Zerg do reach the 2nd hatchery and an extractor, they easily have built up a powerful economy of drones. With a 3rd hatchery later on, armies of hydras can easily be created. Simple group of 24 hydralisks, can easily defeat any player. However the Zerg are very gas dependent, and it does put the Zerg at a disadvantage, since they must expand constantly to maintain the amount of units they can produce.
With a newly founded expansion, protected by sunkens and hydras, you can begin to access more powerful units. First one your list should be queens, they give you good scouting, and the ability to slow down an opponent with Broodling. Lurkers are also accessable. These are deadly now since they're is still a lack of detectors. A spire is one of the Zerg's key structures, and can cripple a Zerg if it's destroyed. Mutalisks do very well, due to their mobility, and ability to be created quickly. Hydralisks can benefit at this point by upgrading to 2/2.
Basically, this is the point where the Zerg expands like crazy, taking many sites, due to the fact the sunkens and spores can hold their own. The Zerg also gain the ability to transport mass troops, with all the overlords they have lying around. This allows for a backdoor entrance to many bases. This is where the Zerg usually win, because of all the expansions they hold. Also this where the Zerg lose, if they can't hold the new bases.
The Zerg finally get 3/3 upgrades as well as Guardians, defilers, and adrenalings. First Guardians pose a great threat to another Zerg player who chose to create more land units rather than air. They aren't too effective against a terran, given that they have irradiate, and goliaths. They are also not effective against a Protoss player who has plenty of Psi Storms. Defilers are very powerful against a Terran opponent. This is because the Terran's only defenses against dark swarm, are firebats, irradiate, and siege tanks.
Also defilers are very useful for taking out battle cruisers. Lastly, we have fully upgraded zerglings. These new adrenalings can deal the most damage to anything faster than any other unit in the game. They are very cheap, and it's very easy to create well over 50+ zerglings. There aren't many things another player can do excpet block them off at a choke point.
The Zerg benefit greatly form the new sunkens. This allows them to expand very easily and safely, which is somthing that the Zerg shouldn't be able to do. The Zerg also gain the Lurker which helps to establish a good defense. Also cheaper hatcheries means more expansions, and better unit production. Also the game now has many cloaked units, which won't affect the Zerg, since their overlords are natural detectors.
The Zerg still are the easiest to use, and quite possibly still the strongest on most ladder maps, where the zerg can easily get a quick 2nd hatchery and then sunken up. Also zerglings are very effective, especially with the adrenal gland upgrade. The mutalisk slow down won't affect a zerg player too much, since they can safely create a stronger economy now. Spore colonies are now very effective against mutalisks, meaning less muta rushes, and more hydra mobs. Expect to see more zergling / muta combos since it's still very effective.
