So I hear a lot about how broken Terran is against Zerg. And that's just complete crap. The problem is that people just want to 1a2a their army and expect to win every time because they have "THE HARD COUNTER!" I don't want to do too much repeating as I plan to make a guide of common myths that newer players believe, but a lot of those will be in this guide.
Why is Terran good against Zerg? Tanks; while sieged they DESTROY lings, banelings, hydras, infestors and unseiged do very well against roaches. And what's the Zerg answer to tanks in order to just 1a2a them? Broodlords and Ultralisk (T3 units).
So what's the solution?
"Don't attack them directly!" WRONG, there are several ways to attack them directly, just not by 1a2a-ing them while they're in siege mode. If you drop on top of them or come up from under them you'll be just fine. However, yes this does mean you have to actually outplay them meaning newer players are going to say, "But it doesn't take any skill to his the siege mode button and you have to know how to use roaches to kill tanks." Yeah, true and I'll get to that. But I think most people get that part by now. They just have trouble living that long. "Muta harass and take advantage of their immobility." While that is true, that requires you to get a bunch of units that are terrible against mech when you ultimately do have to face them directly or when some a-hole puts up 20 turrets all over the map.
That brings me to my favorite build :) Zergling > Infestor > Ultralisk (ZIU). Here is the open to the build. 14 gas, 13 pool, drone to 15, ovi, shortly after the pool should pop. At this point make a queen and get ling speed. Make 4-6 lings, then 1-2 more drones (depending on how many lings you made). Expand at 21. When the queen pops out make another and start spreading creep the connect the two expos. Toss down a few crawlers at the expo. Power drone to around 35-40 supply.
You'll notice that you end up with a lot of extra minerals here. So, once the expo is up, start the lair, but keep making queens from that expo hatch. You'll need them in a minute. You'll still have a lot of minerals left since you're just making zerglings, drones, and like 4-6 infestors. This is where you want those extra queens (2 per hatch, so 4 queens off 1 expo and 6 off of 2 expos). Those guys are GREAT for spreading creep all over the map. But why stop there. Use those extra minerals to throw down more crawlers and all that creep to start pushing them forward and expanding your real estate. I typically do this crawler contain with about 8 or 9 of them. I usually like to start melee and armor upgrades level 1 before I start my hive.
So once the 3rd expo has at least started, I start my hive. Also, at that 3rd expo, I always get the two gas first before I start mining minerals... even if it's a gold. You'll see why when you use this build. You have A LOT of minerals laying around (hence like 8-9 crawler push) and a lot of extra queens.
*A quick note about the crawlers. As I said before, tanks are REALLY good against zerglings and infestors. So any early tank pushes can be really scary since you won't have ultralisks out yet. But a unsieged tank is actually quite terrible against zerglings. The crawlers are an excellent way for force the tanks to siege and unsiege to kill rows of crawlers. When they're unsieged and on the move to the next set of crawlers, rush in and swarm them with a ton of lings.
Once you get the hive, the play here is obvious. Start upgrade 2/2 and build the ultra den. You'll want to take a 4th base quickly after getting a few ultras to defend any impending attacks.
Ultras are extremely strong against terran mech, but that said, you still doesn't want to try and run up hill through a small choke in to a bunch of tanks. So, while you can pretty easily run over expansions and engage a mech army head on in an open field with the beloved 1a2a3a, you might still need overlord drops or worms to break in to their main.
Now, you have to know what this is bad against too. I think that's pretty obvious - fast banshees. If they do fast banshees and you don't see it coming, you're pretty much dead. And that brings me to 3 important other things to note.
1) Terran basically goes MMM, Mech or Air. Mech is what this was specifically made for. And we know it's terrible against fast banshee. What about MMM? Well, there's a slight alteration you need to make. Banelings. This seems obvious but the next two points I'm going to make explain why banelings are so good; beside the fact that baneling/infestor/zergling blows MMM to hell.
2) Banelings are a great "alteration" to the build to take care of something I scouted (i.e. he's not going mech). Note I'm calling this an alteration, NOT A TECH SWAP. Tech swapping is changing your plan in order to HARD COUNTER the opponent, regardless of the time/resources investment. Banelings require a Spawning Pool [X] "Got one!", and Zerglings [X] "Yep, got tons of them." So the only thing I have to do is make the 1 building. Note that I'm not saying something like "If you go fast voidrays and you scout his mech play, switch to immortals." Why not? a. you already made the stargate b. you have to make a robo facility c. you can't just make immortals you need more gateways to support them. That's a hell of a lot more of an investment than, "Oh, lemmy toss down this baneling nest real fast."
3) The whole counter/swap thing brings me to my third point, about scouting. If you're good at a build (part a), and you know what it's bad against (part b), and you know how to fix it if you see something different (part b and a half), why do you need to put tons of effort in to constantly spying on them, knowing exactly what they're doing all the time? All you need to do is KNOW WHAT YOU'RE LOOKING FOR WHEN YOU SCOUT! Don't just do it because you saw TLO do it. Do it with a purpose. "But the purpose is to know what they're doing!" WRONG. You know what you're doing, you know what it's bad against. All you have to do is just know what they're not doing (part c). When I scout a terran I couldn't care less if I see a rax with a reactor or tech lab. I know this means they're not going fast banshee. That's all really need to know. I know that I'm safe from the one thing that will end my life, COOL! So I can go back to my build and make sure I get my timings right and that I macro up. Later I'll poke back in and make sure they haven't done anything strange. But for at least the next few minutes I can just build stuff.
Do these things and not only will you see your play improve but you'll also see that ZvT is actually in Zerg's favor because they can pretty much go 1 build and beat 80% of what terran can do.