This particular matchup got its bad reputation from StarCraft: Brood War, where games rarely last longer than 10 minutes, and the only combat units one would see are Zerglings, Mutalisks, and Scourge.
In StarCraft 2, there are some similarities, but also some differences.
For starters, Zergling play is a lot less frequent in StarCraft 2. This is because Roaches, a new Zerg unit, just beats Zerglings so easily that it is not as cost-effective to build Zerglings as it is to build Roaches, despite the fact that Roaches cost 25 gas each (they cost as much as SC1 Hydralisks at the moment - 75 minerals 25 gas 1 supply). The default 2 armour of Roaches also makes Zerglings fairly ineffectual against them, unless in great numbers.
Because of this, the early game of a StarCraft 2 Zerg vs Zerg is dominated by massing Roaches.
If one player tries to get Zerglings, they will be killed by Roaches and then that player will, himself be defeated. If one player tries to tech, she won't have many Roaches and will be squashed by the player who stuck with churning out Roaches early in the game.
A video of me microing Roaches and Hydralisks with Burrow vs enemy Zerglings.
The monotony of Roaches only breaks when players tech to Lair. Despite the power of Roaches, there are three main incentives to tech to Lair:
- Burrow upgrade for Zerg. This allows Roaches to Burrow, but Roaches also regenerate extra-fast while Burrowed, allowing you to combat a greater number of enemy Roaches with fewer of your own.
- Overseers. You can only build these guys upon hitting a Lair, and you need them to detect enemy Roaches in case they have Burrow.
- Hydralisks. These are one of the most important units in Zerg tier 2, and they're the first unit to break up the otherwise pure-Roach army composition of the early game.
Hydralisks are essential because they have 5 range (6 when upgraded). Roaches only have 3 range.
This means that once you reach a certain mass of Roaches, they become rather unwieldy and will become stuck behind each other, unable to actually attack the enemy due to their short range. Because there isn't a whole lot of open space in the maps of StarCraft 2, this issue can be quite noticeable. Therefore, you need Hydralisks to ensure that your damage output is maximised against the enemy at all times - you want as many of your units dealing damage as possible.
However, Hydralisks are fairly frail and Roaches are very powerful against them. Despite their superior damage output, Roaches will very easily beat Hydralisks for cost, but a mix of Roaches and Hydralisks will beat a pure-Roach army.
A video of me (the red Zerg) defeating a pure Roach army by using a mix of Roaches and Hydralisks. Notice how a good deal of Blue's Roaches don't see combat until his front line has been destroyed.
Mutalisks are only useful if you can catch your opponent completely off-guard, but most Zerg players immediately go about transitioning into Hydralisks upon reaching their Lair. Given how effective Hydralisks are against Mutalisks, it makes going for Mutas in an SC2 ZvZ a very risky prospect. More often than not, it is your opponent who will come out the better for it.
In the ZvZs I've seen and played thus far, games can certainly end quite quickly. As with Brood War, there seems to be little margin for error, as even small mistakes like losing your starting Overlord to the enemy's Queen can set you back quite a bit.
However, it is also not too uncommon to see Zerg players taking their natural expansion and the game lasting for a decent amount of time - certainly longer than the 10-minute average of a Brood War ZvZ at least.
I have yet to see a very lategame ZvZ, but I'm curious to know how it'd look like. I believe that after Roaches and Hydralisks, Infestors are the next combat unit to shake things up. Fungal Growth is useful for tying down enemy Roaches and Hydras, preventing them from getting into combat and doing decent damage in an area.
Based on early Beta impressions, ZvZ seems like it has the potential for much longer games than in Brood War. Although massing only Roaches in the early game may seem boring, it's worth noting that there was very little variety in Brood War ZvZ to begin with, and I believe that SC2's ZvZ, like BW's ZvZ, will be something of an acquired taste.
