I got SC2 on opening day. I am no stranger to RTS games. I have been playing since opening day. Tonight I went through the "division league" matches. 3 out of 5 I played against Zerg. All 3 I lost in about 5 minutes. I literally had only enough time and resources to create 3 marines and my opponent had 7 zerglings in my base. Seriously Blizzard???
By the time a player has lings, you should have a wall up actually. Don't blame Blizzard, just learn new tactics.
Don't worry zergling rushing only happens in the newer division because Blizz makes countering rushes easier than the rush itself. Build a barracks and 2 supply depots to block your ramp. 2 of the expert challenges have a zergling rush situation so you should also try them out.