I'd just like to point out several observations I've had in relation to Zerg in SC1 and SC2.
Choke Points (200/200 Army Fights)
In sc1, it was viable for a 200/200 army of zerg units to go up and attack either a terran or a protoss who was simply defending in their base. This 200/200 Army if it included Defilers would definitely be able to at least stop the terran or protoss from mining or pushing out and attacking except through dropship. With solid micro the attack could possibly destroy their whole 200/200 army of defense.
For those of you not familiar with SC1, Dark swarm allowed all zerg units burrowed underneath the area it was cast on to not take damage.(In ZvT The only thing that could hit them would be Firebats or Irradiate, I'm not talking about ZvP here) They also had an ability called Plague, which would bring every unit it was cast upon (except a few) down to 1 hp. These AoE (Area of Effect) spells allowed Zerg to match up with the Terran and Protoss equally in end game tech.
If there was ever a small choke, think Destination and those 2 little ramps into the natural base,(If you don't know destination, simply think the area leading up into Steppes of War's Natural Expansion) the zerg could defend it very well with lurkers and sunkens, our 2 ranged damage dealers. If you threw in Defilers you could defend or attack from those two little ramps. I'm not going to discuss that you could attack with Guardians, because you can do the same with BroodLords. However in SC2 there is no unit that provides a solid "Choke" fight vs. Protoss or Terran. To explain this point better, if you can fit 10 units across and your 10 units will be fighting the opponents 10 units you will have problems. There is no unit composition of Zerg's that will come out on top with these 10 unit vs. 10 unit fights. I'm considering both sides have equal upgrades and a fairly even level of tech. The reason this is so, is because of the incredible range of both Protoss and Terran.
Zerg's several ranged units are as follows : The Roach (3) The Hydralisk (5-6) The BroodLord (9?) The Infestor (5-9) The Mutalisk (5?) and The Queen (3-6). The main abilities these units can use are simply to attack. Hydralisks have high DPS, roaches have high armor (1 lol), Infestors have a strong AoE bind and a mind control ability, Broodlords have the best ability to constantly produce dps and tank units. With a proper combination of units, Roach Hydralisk BroodLord and Infestor vs. Protoss or Terran you will have a very strong ranged force. If you toss in ultralisks as tanks you will have the strongest zerg army at attacking a fortified position.
Now lets discuss what other races can do, that will enable them to turtle comfortably no matter what you as a zerg throw at them.
Terran : The Wings of Liberty have apparently freed the terran to have a unit to counter each of the zerg's units. They have Marauders with Tanks, Thors, Vikings and Planetary Fortresses to defend. These units when used with any sort of micro (Healing / Sieging / Stim) Will be able to stop a much MUCH larger zerg force. Tanks have such a large range as with vikings that no matter what unit composition you throw at him, he can remain in his position and hold Especially well if your attacking a small choke point. His tanks will deal AoE damage, his Thors will tank all of your damage, along with marauders. (Both of those units can heal faster then a roach burrowed (Think medivacs, scvs)). I havn't even mentioned the Planetary fortress in defending.
While attacking a planetary fortress you will literally need a HUGE army to defeat it. The terran can simply heal it while moving his army to pick off your units as they have concaved around the Planetary. My point here is that against a terran in an equal space their units will almost always have the advantage. Zerg's CANNOT push terran's in a proper choke back!
Protoss : This I don't see as quite as much of a problem as I do with terran. I feel like Protoss doesn't have too strong of a counter to broodlords, ultralisks and hydralisks if properly proportioned. However I will say that with Immortals, Storm, and Collosi they can defend a small choke area Very Very well. So it is possible to push a Protoss player back and do some damage. We can also dropship against protoss. We cannot dropship against terrans, because with several sentry towers the terran will be able to see the drop coming and plan accordingly. I think the match up of ZvP is fairly well balanced and we will have to see how early game works out, and how large armies will fight.
The point of my observations, is that in SC1 Zerg had a viable unit to delay mining and push a terran or protoss player back. The defiler allowed the zerg's army to have almost equal strength or higher strength then that of the Terran or Protoss. I feel that if Zerg doesn't get something that will allow us to both attack and defend small choke points (Broodlords? Yes in ZvP, Not so in ZvT -- Ranged on Vikings is exceptionally long)
then the Zerg vs. Terran match up will continue to deteriorate into Zerg's such as myself whining about more things then just choke points.
Thanks for reading, Sheth
For a Replay Showing the Choke Advantage Here's One :