I thought the story was supposed to be darker than the SCII trilogy (that's what I'd heard) but so far the presentation's still pretty silly. It's not surprising they chose to make Nova the main character since she's probably the most compelling non-main character out there and also this will appease the people still pining for Ghost.
Spoiler: show
I am a big fan of the new tileset stuff going on, especially that Tarsonis building interior in map 3. The gameplay isn't always the best (that vulture driving sequence was soooo quirky and minigamey) but I will say that it's a welcome shakeup from the usual SC2 mission structure of Do This Thing Three Times.