zerglings, how can you play a zerg and not use it? they cheap and easy mass and they are very good meat shields.
the latest patch made pool cost 200, so it kinda screws up your economy when u go for 6d pool and even more in 5d. early game 6zergling rush can make good distraction on your enemy and can even destroy them if you micro carefully (attacking all together, watching individual ling's HP- when get hit you pull back, etc). usually enemy probably has like 1 zealot or 2 zealot out, and with 6 or 8 lings if u micro well u can kill those zealots and lose only abt half your troop (assuming the P player doesn't micro).
burrow + speed + attk speed (late game) are zerglings best friends. against goons/marines, burrow = most effective.
u don't have to crush enemys entire army in 1 wave to win, you can kill their units in diferent waves while preserving most of the ones you have. like, if you see the guy has 8 zealots and you have 2g of zerglings (24 lings), u will probably lose if u fight those 8 the same time, another way is to "lure" a partial of their entire army and deal with the 8 in 2's or in 3's, so he'll be losing a lot more than you're losing, eventually you will have more units and you will be in the upper hand (assuming u don't let him expand, you mine resources well, and keeps up with production) This game is all about macroing.
just my opinion
Chilam-
P.S. (Im always looking for games, you can find me as Chilam- either on US West or US East, I usually play on West.)