When playing with the Zerg, you have to out expand your opponent, especially on island maps. As of now, mutalisks aren't dominant air units as they once were, especially with corsairs. So keeping a ground game with hydralisks is a good idea. Now you must perfect your build order, only to because the Zerg are the slowest to expand on an island map. So research sacs and speed as soon as possible. Holding large islands, as your main base, is a hard thing to do with the Zerg. So once your island expansion is built, try to build your key structures there since it will be better defended. Getting to a hive is also important, because this will allow for nydus canals, making transferring of drones easier.
Now when you have your lair, you get two choices. You can either hydra/zergling drop, or go for mutalisks and scourges. Queens aren't really an option here, except is they have templars, but later they are needed. I would rather build for a hydralisk drop, only because it has more potential for killing an opponent than mutalisks. Since everyone expects air units, turrets and spore colonies aren't going to effective against your hydralisks. You should pack a group of zerglings as well, only because you will have extra minerals, so zerglings will do a good job of drawing fire.
Key structures to build are the evolution chamber and lair. You need an evolution to create spore colonies, which will help to restrict any air traffic and drops. You also need the lair to get the upgrades and access to the spire and queens nest as well as the hive. Make sure to spend the time to create a good defense for your island expansions early in the game, because it's hard to defend without a spire at this point.
Now if you plan to go all hydralisks and drop your opponent, don't change your plans. This is bad idea, and will cost you the game, because you have to spend more resources on getting a spire and then guardians. On the other hand, if you have mutalisks and zerglings, don't change and build hydralisks. Either way you must contain your opponent and out expand him as well.
Whichever choice you make, try not to lose your small island expansions, since they're easy to defend. However expect to get hit hard on your large island bases.
Personally I like hydralisks, and hydra drops since they are one of the best anti-air units, and can hold there own against photon cannons and bunkers.
