Pretty standard affair for a "Starcraft II game"
Because of the Kerrigan-centric take in the HoTS campaign, the storyline/pacing is extremely straightforward (revolving entirely around her personal revenge). It's a standard Blizz RTS affair; pretty visuals/CGI, fun units/standard SC-gameplay, and a 'meh- it's ok' story that's just good enough for you to carry on to the end. Actually, relatively, it's slightly worse than the original SC2 campaign storyline. All in all, most of the plot is extremely predictable, and nothing really 'happens' with regards to character development or anything special. In the end, everything kind of deflates, in an extremely underwhelming matter. It really doesn't get anymore predictable/simple than this.
Still, the game was fun enough to play, and it has Blizz production value. The addition of Kerrigan and her strong-moveset made her an integral part of the 'game'. Focusing on her alone many times was much more important than any other group of units, especially as she became increasingly overpowered. Personally, I found it to be a fun addition to the game, although I could see it turning some people off due to the switch from a strict RTS to an action RPG-ish kind of feel.
Ultimately, not great, but not bad either, SC2 HoTS is a standard Blizz game that's pretty much what you expected. Nothing more/nothing less.