no special campaign units were given the zerg
So...Abberations, Impalers and Lurkers aren't special units? Not to mention the Evolution Chamber mutations of the Zergling, Baneling, Roach, Swarm Host and Ultralisk.
And to be fair here...WoL may of had A LOT of "special" campaign only units, but most were either useless, or overlapped by better units.
the Overlords were reduced to nothing
I kinda agree here. However, Overseers would of been kinda useless in the campaign, because they are designed to be a harassment and spy unit which just doesn't translate well against an AI enemy. Add in the fact that Blizzard simply refuses to allow enemies to use "cloaking" so there would of been no point in having it for detecting. And as for transporting, with how they designed the missions, you really didn't need to use transports for anything. Even in WoL, the only time you really needed transports was for the Moebius rescue mission.
Nydus Worms weren't even useable
This is quite understandable. Nydus Worms would of made some of the missions too easy to complete. Just think of missions where you would of had to destroy a structure. You could simply pop a Nydus Worm nearby and cheese it almost instantly. There's also the possibility of it breaking cut-scenes and what-not for going somewhere much earlier then your suppose to.
This one is kinda odd. Mabye Blizz thought that Vipers overlapped with their role as anti-air here, but if you look at the campaign, you'd notice that Zerg had practically no anti-air. Corruptors, Scourge, Devourers and even Vipers if you chose the Brood Lord mutation would of been out of the picture. Almost like Blizzard didn't want aerial battles in the campaign. But, I'm just gunna go with Blizz thinking that Vipers overlapped with the Corruptor's role.
The story was rushed there were no real choices in the story.
The story was definitly rushed. No doubt about that, but "choices" I think don't really work well in RTS. At least not in the way Blizzard's been doing it. WoL, the planet choices made the missions between Mar Sara and Char all disjointed and stuck in place, feeling like nothing was getting accomplished. And the missions where you had to side with someone (Haven, New Folsom) were freaking terrible (they don't even play a role in HotS).
HotS does it somewhat better since the planets are now in arcs, but really, there's nothing different aside from Kerrigan having her Zerus form or not in some of the cut-scenes. The story also actually feels like it's moving this time around since it's more linear compared to WoL. Making the planets have "arcs" was probably Blizzard's best decision so far towards the campaign.
And I was especially hoping for a wide branching story like Keriann gets to choose between staying a terrain or becoming a zerg giving the campaign much replayability like WoL and its alliances and unit choices, I don't even think I used most of the upgraded units I got.
Again, branching just isn't going to happen. At least not with the current Blizzard. They attempted it in WoL and failed miserably, and didn't even bother to attempt to improve on it in HoTS. But honestly, I think branch storytelling just isn't there yet. Even Bioware who people claim is the king of branch storytelling doesn't have it correct yet. *points at Mass Effect 3*
It will definitly be an award winning game the day a company makes a game that actually branches into two different storylines, and not having just simple choices like if this person should die or not, or what pathway to take to an end mission objective.