Terran:
Nuke landing time has been decreased from 20 seconds to 5 seconds.
Units must now return three times a day to the barracks, factory or starport that they were spawned from in order to eat, bathe and sleep. Failure to do so will cause irritation in your soldiers who will then go AWOL to live peaceful lives with the native women.
Firebats are back in the game, and you can combine one with a Marauder to create the Firauder, who shoots grenades that explode into FIRE.
Your mineral income is now dependent on whether or not fat politicians sitting comfortably behind secure walls think the Zerg are a real threat. They will bash you for spending millions of minerals on the war while at the same time demanding to know why there aren't enough combat shields to go around.
Lifted buildings can now be landed on top of small enemy units, squishing them.
StimPacks now slowly cause addiction in marines and marauders. They will ransack your Command Center and rob SCVs for money to buy more.
Vikings now have Norwegian accents (Blizzard I don't know how you fucked that one up.)
A new Terran unit has been added, a massive warship called the Iceberg. It moves extremely slowly but deals heavy damage. When summoned from the Starport it will shout out in a thick Mexican accent: "ICE to meet you!!!"
Battlecruiser models are now to scale.
Protoss:
High Templar now have French accents.
Motherships can now land in a manner similar to vikings, becoming a portable Nexus that probes can deposit resources in like a normal Nexus.
Photon Cannons have been removed from the game. I don't care if you need a static defense, those things are fucking retarded.
If a pylon is destroyed while a unit is warping in, instead of that warping unit disappearing it will instead half-warp in, its mangled legs trying to find footing and its misshapen lungs gasping for air before flopping over to one side and dying a brutal death, alone and unloved.
Carriers can now be loaded with Void Rays and Phoenixes instead of Interceptors.
Three Colossi, a Carrier, four Immortals and two Void Rays can now merge together to form PROTOSSTRON, SCOURGE OF THE SWARM. With his mighty fists he tears apart his foes.(Note: an Archon must be available to pilot ProtossTron)
Half of all zealots warped in are now female zealots, and they're fucking SEXY.
Void rays now have unlimited range as long as they have line of sight with their target, because it's a fucking laser beam.
Zerg:
Zergling pathing has been changed so that when running in a group they form the shape of an Ultralisk, this defense mechanism warding off natural predators.
Hydralisks can now ride Roaches, using them as little steeds to cross the battlefield.
Creep now spontaneously generates Banelings, slapping Francesco Redi in the face.
Queens now have psi storm and blink.
Ten Ultralisks can merge into an Omegalisk. Also, ten Overlords can now merge into a Cerebrate that can only be killed by a Dark Templar, but it doesn't matter because all they do is sit around and bitch at Kerrigan all day.
Ultralisks can now move while burrowed.
Zerg buildings can now burrow, forming extensive ant-like tunnel systems. Little holes will begin to pop randomly out of the ground where a stream of Broodlings will attack from.
Zerg can now summon a Leviathan from a Hive, but it doesn't recognize friend from foe and just goes batshit crazy on everything.
When Ultralisks die they now explode into twenty zerglings.
Overlords can now dump creep on top of enemy biological units, getting them all sticky and glued to the floor, ensnaring them.
If Neural Parasite is performed on a Dark Templar, the link to the Khala will shatter and the gross perversion of what should not be will draw the attention of the Voice in the Darkness. A link to the void will open and cause a massive wormhole in space and time, devouring the battlefield and causing a draw.
UPDATE
Someone leaked screenshots of my new patch.