Dustin Browder, Lead Designer on StarCraft 2, has written a post on the StarCraft 2 community site about StarCraft 2: Heart of the Swarm's multiplayer, and some of the changes that the game has seen since BlizzCon 2011. Stab yourself in the eye with a stimpack, there's a lot to get through.
On the Terran side of things, Browder mentions that the human race of SC2 has undergone significant changes since BlizzCon. The Shredder unit, which would have been used to spew radiation in a ball around itself, is gone. The Warhound, the smaller, faster version of the Thor, is also in contention. According to Browder, "The shredder was very confusing for players as well as being something that was easily used to kill a large number of workers with little to no warning. It was rarely used for its intended role of map control." As for the Warhound? "It still feels a little too much like a small thor, which is just not new enough to give Terran players new strategies," Browder said.
Since Blizzard only announced three new units for Terran at BlizzCon, this leaves only the Battle Hellion still on schedule to release with the game. However, Browder did say that they're experimenting with adding more units to the Factory and if they keep the Thor unit (which they better, it's my favorite!) then they might implement an anti-air spider mine, " that would give the Terrans a way to get some factory-built anti-air into small places that a Thor has trouble reaching (like near your minerals)." The team's also experimenting with a long-ranged missle launcher which could be used to break siege tank lines.
The Protoss have fared much in the way Terrans have since BlizzCon. According to Browder, the Replicant, the unit that created a copy of other units, has been cut and the Tempest has been reworked. The Replicant was cut because, "he was causing enemy players to not build certain unit types and was actually removing diversity from the game instead of adding diversity."
The Tempest was reworked since Blizzard upgraded the range on Phoenix already, so they felt like they no longer needed a splash anti-air weapon. Now, the Tempest is working as a long-ranged aerial siege weapon that can hit both ground and air units. This will allow the Protoss to force engagements rather than sit there massing up a death ball.
And now we reach the Swarm. Luckily for all you little Zerglings out there, the Zerg have remained largely unchanged since BlizzCon. The only change is that the Viper has been given new abilities, making it more of a pure caster than a utility unit. "In addition to Abduct, the viper also has the ability to blind biological units in an area of effect. Blinded units have their range reduced to 1. This is obviously effective against Terran infantry as well as Zerg roach and hydra armies. The viper can also regain energy by feeding off of minerals. This locks up the mineral patch and prevents it from being harvested, so you want to use this ability away from your base," Browder said.
With this change, Blizzard's going to reintegrate the Overseer to make it more interesting. They're also toying with new ideas regarding Nydus Networks. So far they're throwing around ideas like allowing you to spawn different types of worms, having a worm that can spew creep across several screens, and having a worm that only attacks enemy buildings. None of those have been implemented yet, though.
And there you have it! I think that at BlizzCon a lot of StarCraft 2 gamers, both casual and professional, were a bit worried about these new units. How would the game be balanced with a lot of them in the game? Now that Browder's written this update, they seemed to have calmed down a lot and are back in the Heart of the Swarm corner.
Unfortunately, they might be there a while as the game still has no release date. Browder's promised that the team is working as hard as they can, and it will be released as soon as it's ready.
Source: StarCraft 2 Blog