Since there are multiple threads that detail the specifics of the new units, I won’t delve too deeply into those, but try to open a discussion on a broader scale. You can view a good one here.
A broad theme that Blizzard seems to be approaching going into Heart of the Swarm is increased board control. Many of the new multiplayer units introduced attempt to give a player more ways to exert control over map positions, either through strategic unit placement (Widow Mines) or by forcing the enemy to defend against a sieged position (Tempest) or against multi-prong harass (The Oracle.) To a lesser extent, the Viper can lock down small pockets of the board as well with Blinding Cloud.
Overall, granting the player ways to exert board control is a positive step towards a more balanced game; when positional play is encouraged, the more strategically minded player is favored. This is a good thing.
Another theme Blizzard has been exploring is giving individual units a lot of specific use. The Oracle jumps to mind as a unit designed to do specific and narrow set of tasks. It cloaks units, disrupts mining, and grants scouting. The Viper is another that has limited specific uses; it disrupts player positioning in multiple ways, through Blinding Cloud or by abducting enemy units. The Tempest can siege a position with its staggering 22 range and . . . not much else, with its pathetic damage-per-second.
I’m more torn about these units because they are so narrow in scope and lack gameplay diversity. A unit like the Oracle is a cool addition in terms of its toolkit but its abilities don’t complement each other very well and it doesn’t allow the player a lot of creativity. It cloaks units in a large battle, but the other abilities won’t be used.
Unlike the Infestor, I don’t see the Viper doing much outside of teamfights (besides being a leech, literally!) The Infestor is a really interesting and diverse unit because it has multiple different roles it can occupy – it can support an army, deal ridiculous damage, lock down units, harass bases, and defend bases. It’s a multiple-use, high skill, high reward unit.
In general, the more specific of a role you create for a unit, the less diversity in gameplay it will offer.
Lastly, Blizzard seems to be overhauling existing units to increase their effectiveness. What I mean is that instead of complete redesigns or introducing units better suited to a task, Blizzard is giving units already in the game more expansive roles. For example, Hellions now can transform into beefier Firebat-esque units, and Ultralisks can now burrow charge into battle.
These changes should help increase viability for certain builds and strategies, but they also mean that current designs for those specific units are fundamentally flawed.
Overall, my review of Heart of the Swarm seems critical if not negative, but that’s far from the truth. I think some of the changes and unit introductions are very cool. In fact, some of the units like the Widow Mine offer gameplay reminiscent of Brood War. Ignore for the moment the ridiculous damage, which is something that can be tweaked before release. This type of unit offers a lot of deep gameplay options: it can offer board control, it can harass, and it is high risk, high reward. It has the potential to devastate an enemy’s army, or could be absolutely cost-ineffective if the enemy controls his units and defends against the mines well. These scenarios are the ones that bring fans to their feet while watching Proleague, OSL, and GSL – the type of situation that sets apart the pros from the pretenders.
Starcraft II: Heart of the Swarm has the potential to be a very fun, highly competitive expansion to Wings of Liberty, especially if Blizzard can design units that, in the hands of a revolutionist, can change the way people perceive and play the game. Only time will tell.