I will discuss the modern bo's, some variations, reasons for the bo's/decisions zerg gamers make and leave the rest of the topic open to discussion.
I am not the greatest zerg user. Some of you may even think I suck, and that is a perfectly valid opinion. But lets leave those comments outside of this. Rather, lets focus on aiding fellow gamers
ZergVsZerg:
The Basic Build Order/Tendency:
ZvZ has broken down into a hyper aggressive game. No longer do you see the fashionable macro style where the extended distance between bases allows for 12 expand. Today you ask yourself 1 of 2 things, do I want to attack or absorb the attack. This is the dice we roll as modern zerg players. 9pool speed is the standard. I shouldn't have to tell you the build order so I will only discuss the post bo phase. After 100 gas is mined pull 1 drone from the gas and have it mine minerals. Macro at this point is crucial, the misnomer is that 9pool speed is an "all-in build." It is not. The mentality is that you want to risk winning with the mentality that you will create a fragile game style where the player opposite of you must react perfectly or face an unsurmountable strategic disadvantage. You do this in one of several ways, all of which call for scouting and proper "game sense." If the other Z has expanded and cancels you should pressure the base. Do not allow yourself to engage lings near the mineral line unless your advantage is clear and the battle is a mere semantic. Instead focus on picking off crucial drones and outnumbering spawning lings. If the Z has 12 pool'd you must put another drone on the gas (3) and begin to macro at home with a quick lair. This is so that you can possibly get the zerg to overreact by making a sunken/more lings and consequently be being in lair tech. From there you will pressure with the tech alone, forcing them to cut drones or make spores. Respond by massing ling or macro'ing respectively. Most common however is that they themselves 9pool speed. This is where ZvZ becomes a fascinating chess game and battle of wit/balls. You can engage this in several ways. One is to maintain the ling army and either guard your own ramp (from the top) or pressure him at his. The idea here is that you will lead out lings from the ramp and with superior positioning/micro win the ling battle by maintaining stronger control. Another reacttion is both players observe the other with their overlord(s) and simply shift into a macro game. No advice necessary for this specific situation since it is a standard ZvZ situation. Another response is to cut lings yourself and instead depend on the ramp position to make up the slack. From there you macro and hopefully take advantage of the extra 3-4 larva your opponent used to make lings.
ZvZ Mentality:
As I said earlier ZvZ is in its most aggressive evolution yet. With the overlord trick scourge are relatively useless (in the 3 hatch scourge/ling form). They are however, not obsolete. As discussed in my previous Strategy Guide I recommend standard mutalisk armies with a secondary force of scourge. I usually time this (after my 12 pool -> gas -> macro/hatch) so that when I have around 12 mutalisks (10-11 depending on situation) I can make 4-8 scourge with the surplus gas. The idea is to engage the enemy mutalisk force with my mutalisks while having my scourge force a distance behind. Space them so that they are evenly spaced about a half inch a part. Once the muta battle has begun bring in the scourge force. Tell them to move PAST the enemy mutas. Once they are amidst the mutalisks hit "A" and they will (for the most part) hit enemy mutas 1 per muta. This is one of my favorite tricks and part of the reason I am as successful at this mu as I am.
I advise against overlord picking / mutalisk patrols. We are not progamers. We do not have the 400 apm and micro that makes this worthwhile. In fact the risk of giving free hits to the responding mutalisk force is unequal to the benefits you can get from winning an overlord or two. Instead my advice is to wait for the other zerg player to get anxious and do this. Space overlords around a healthy perimeter of your base/expansion so as to see an attack and respond. Chase the mutalisks as far as it is safe. ZvZ is a VERY fickle mu. Even 1 of these engagements can do enough damage to make the deciding battle a clear victory for the patient zerg.
An easy and very cost effective thing to do is take 4-6 lings away from your force and keep them out of view. If the other zerg player gets overly aggressive you can go get 2-3 drones that can be game deciders with relatively no risk to you. Remember, zerg's are aggressive these days, the smarter reactionary zerg will win. Play like a hacker.
[Ask Questions specifically to the ZvZ section by labeling it as such please]
ZergVsProtoss:
Build Orders/Tendencies:
Gone are the days where we could 12 expand. Gone are the days where protoss were a early threat. Again we find ourselves playing an odd marriage of aggressiveness and patience.
What are good openings vs FE protoss?:
My personal favorite is again the 9pool speed. Pull all drones from the gas after 100. Make 6-10 lings and kill the scouting probe. From here the game is decided by the protoss. If they get cocky and rest on 2 cannons and proceed with expansion you can overrun with 12-14 lings, easy game. If they block with a few probes and expand (and you can run by) do so, run by. If they completely seal the expansion in by blocking it with probes kill scouting probes and double expand / macro as usual. That being said MOST p's will respond by delaying their expansion and making 3-4 cannons. This is great because you have now secured them a no scouting situation and can have equal macro->better depending on how paranoid they are of your aggression.
Another opener that is more macro oriented and safer for the less comfortable of the 9pool speed is the 12 pool 12 expansion. This is reactionary again. Safe against a cannon rush or proxy gate but also able to match/exceed the protoss macro depending on the Z's style.
Some Z's still brave the 12 expand (map permitting of course). This is unwise however because the modern PvZ consists 98% of the time with an FE, and with minerals the way they are a blocked cannon rush is almost ALWAYS a possibility. Couple that with the 2nd most common P opening, proxy gate, and you have a mathmatical nightmare for the greedy zerg player.
How do I react to the standard Bisu style?:
There are a couple ways to approach this. One is a "Mondragon" esque approach and slap down a fairly early evo chamber to A. upgrade faster and respond to the +1 z lots B. make a spore to guard the overlords from the first sair. Or you can make a hydra den. Personally I prefer the hydra den as it allows me to gauge the situation. If they are cocky and dont cannon up its game over. If they go mass sair I needed the hydra anyway. The trick is to not go TOO hydra heavy if the situation doesnt call for it. It is important to secure that 3rd gas and advance to lurkers so as to slow down the z lot heavy army. Once the 3rd gas is secured I usually go 3 evo chambers. Probably the most effective response to bisu style is a strong macro style that is "sauron" in nature. Allowing the lurkers to cut up the z lot heavy army while the hydra/ling mind the tech units.
Lots of protoss will couple their attacks with a DT drop. This is especially effective because the assumption is that you are overlord condensed or unexpectant of the attack and thus unprepared. Be prepared! Its fairly common and can turn a clear win into a loss right before your eyes. Sunk/Spore is enough to buy you time to respond. The especially wary will add a few scourge and some hydra just to be safe.
Mind your expansions! The DT is in vogue. Spore/Sunken each expansion, especially main's natural expansions if you should secure one. One of the ideas behind the bisu style protoss is to take advantage of the DT cloak, dont allow them that comfort.
Remember to play the style of game the mu calls for. You dont need to do doom drops, harrass with muta or constantly pressure with your army. You need to limit the gas heavy army of the protoss to its natural base or perhaps 1-2 more (game length/style permitting). The idea here is to lean on their economy with your swarming army and make them spend their resources on thwarting your pressure. The bisu style tries to be as cost effective as possible. If you can mind the sairs/templar (including DT) you can pull ahead and drown the protoss in rivers of gooey zerg guts.
What if the protoss goes speed z->standard?:
This is not too uncommon from what we would do in the past. Standard games these days however often involve late game switches. Protoss no longer feel the need to remain staunch in a unit mix. Expect corsair late game or even reaver artillery. So what this does for us zerg players is we need to account for this, even preemptively by making a hydralisk den (not just pure ling/ultra) and even upgrading hydra attack. This is crucial. Protoss can _again_ shift the balance of the game by catching a superior zerg army/macro off guard with an invincible DT-Sair army.
Another response that is often negated is plague. DT are fairly weak units, so are corsairs. Late game zerg should involve defilers with an emphasis on plague. Swarm is nice for expansions but when it comes to the DT/Sair heavy protoss force coat it in red venom and watch as A. short term detection is offered and B. immediate damage is made useful. In my last strategy guide I argued against the use of defiler's ZvP, here we see its a necessary evolution as the DT/Sair become more common.
[Ask questions in regard to ZvP labeled as such]
ZergVsTerran:
Standard Bo's/Tendencies
Builds havent changed dramatically for zerg vs terran. 12 Expand is still viable, standard 3 hatch applies. Muta or lurk are both viable.
Personal advice: I like to go drops. With maps like Zodiac, Python and others in rotation.. we find ourselves again with the 1-2 island expansion maps. When T's are doing the standard FE -> 3rax+1 or tank bo we see that they are fairly slow to respond to drop/expand->island. This means you can keep the terran in its main base while you live off of 3 gas and tech to defiler. The tradeoff is great for the Z but it requires patience / intelligence. If you lose a drop or two you can edge the terran into a position where they can counter and win or thwart and be way ahead. Let the threat of a drop be enough.. or the actual drop if the situation permits.
[Like before, ask with tag specific q's]
Lets make this productive:
I know this is relatively short and has less content than the previous guide but I think that is largely in part because there havent been AS many changes as there was worth noting before. That being said, whatever is undercovered I can answer in as much if not MORE detail should you ask a question that requires that much analysis.
Hope this is helpful!
Enjoy~