[Demosthenes]

I think they are trying to hard to find a game shifting unit.
The units in BW changed the game a huge amount but didn't do it in incredibly ridiculous ways.
Like take the lurker. Zerg already burrows.... why don't we let a unit attack when burrowed? Bam!
Most of the HoTS units introduce completely new game mechanics or "spells".
Locking mineral patches? Where the hell did that one come from?
The problem with most of these new mechanics and spells is, I feel, they have very specific uses. They don't allow as much dynamism as BW did for SC1.

That being said, Kezz is right, it IS in beta and they might just be throwing stuff against the wall and seeing what sticks.