Missions are just as bad as the story.
HotS, however, drops the ball entirely. The campaign has some of the most boring and predictable gameplay I've ever experienced in an "RTS".
First of all, let me get this out of the way:
Starcraft II multiplayer is awesome to watch. Watching star players make use of the new units in creative ways is a fresh experience. HotS succeeded in pumping new life into Starcraft as an e-sport.
That being said, gamers who aren't interested in investing massive amounts of practice to at least compete at multiplayer... and who expect the same rich, well-thought-out campaigns that we've seen in Warcraft III, Frozen Throne, and even WoL will be left in the dust.
The entire campaign is designed like a quest chain straight out of WoW. Especially the "creative" missions that the Gamespot reviewer praises... are incredibly linear and easy.
There is no ambiguity to make the missions feel more challenging, genuine, and atmospheric, such as the infiltration missions in SC1. You are told exactly what to do, shown how to do it, and then rewarded for doing what you've been told with shiny superpowers that make the next mission EVEN EASIER.
There is no sense of thrill or accomplishment. WoL, even with poor writing, at least had tight mission design.
With HotS, they've sunk even lower. It feels like a cakewalk, Fisher Price children's toy. Kerrigan is some omnipotent action figure with way too much power and zero personality. You can sense that they hired the wrong writer/designer who hijacked the brand and carved it in his own, pandering image. This is not the original Kerrigan, not the original Starcraft universe... just a blatant, shameless ripoff.
They can't help but put huge glowing targets on the next objective, which you can generally a+click through and steamroll the opposition, even on Brutal.
This isn't the same Blizzard. First Diablo III, now this, and I can safely say they've definitely lost the "Midas touch" that they were once known for.