If I were to start playing Zerg in some multiplayer games, what differences would I want to be aware of before starting?
I know that all the specific evolutions (raptorlings, splitting banelings, etc.) don't carry over, but what other mechanics are different?
Your right that none of the strains are in multiplayer, here are most of the changes I've noticed:
Hatcheries continuously spawn larva up to 9 or 6 (based on difficulty) instead of 3, in multiplayer they only spawn a maximum of 3.
Queens are now swarm queens, who lose the ability to inject larva (this is baked into the hatchery). Their heal costs less energy but also heals for less in the campaign, and is also now on autocast - in the campaign it is an expensive manual cast ability. In most missions, creep tumors are able to create a new creep tumor if the one being morphed is destroyed. In multiplayer a creep tumor only gets one shot at replicating itself, and also costs 50 energy to cast - but does not have a cooldown. Finally, in multiplayer the queen slows to a crawl when not on the creep.
Zerglings can only have move speed OR attack speed, not both, this is baked into the evolution you pick. In multiplayer you can research move speed and attack speed (the latter requiring a Hive)
Overlords Have baked in speed upgrade (normally researched at hatchery) but can not transport units (normally researched at lair). In multiplayer overlords have the abilety to generate creep when not moving. They can also not morph into overseers (which aren't in the campaign).
Spore Crawlers still require an evolution chamber, which was changed to spawning pool in multiplayer
Abominations are not in multiplayer
Roaches Can research tunneling claws (move while burrowed + rapid healing while burrowed) and a speed upgrade in multiplayer, the speed upgrade is not available in the campaign and tunneling claws is an option.
Hydralisks can learn grooved spines (range) in multiplayer but it is an evolution option in the campaign and also have the Muscular Augments upgrade in multiplayer increasing its movment speed by 25% off creep.
Mutalisks have none of the evolution upgrades available in multiplayer, they can also not morph into anything in multiplayer
Viper is morphed from larva after creating a Hive in multiplayer, instead of being a mutalisk morph
Corruptors are not in the campaign. Corruptors are built from larva and are an anti-air unit, they morph into brood lords (instead of the mutalisk in the campaign)
Infestors's fungal growth is now a projectile in multiplayer, and neural parasite must be channeled to control a unit in multiplayer, unlike the campaign in which the control is permanent. Infestor's also do not have consume in multiplayer, but do have Spawn infested terrans.
Ultralisks have no abilties in multiplayer and can only gain +2 armor in multiplayer, which doesn't exist in the campaign
Swarm Hosts can burrow by default, and have no extra upgrades (their locusts can only attack ground)
Lurker is not in multiplayer at all, the hydralisk den does not morph into a lurker den.
Nydus Network is not in the campaign.
In Multiplayer
Your hatcheries will only spawn 3 larvae. Swarm Queens replaced with regular Queens, which have an ability to spawn an additional 4 larvae at a hatchery for 25 energy.
Several of the mutations (not the evolutions) are available as upgrades purchasable from the appropriate buildings.
I'm sure there are more, I will add to the list when I get a chance to return home and test.
