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. "