Figured I would post my own little opinion on the single player game since I got to try it out at BlizzCon.
All I have to say is, awesome! People complain about how Blizzard is splitting it up into three games, but even just having two levels open to me showed me why, the game is going to be massive in design and story. They improved the graphics of the in-game cut scenes since I saw them last, with better mapping and shading, I swear I felt like I was watching CGI sometimes.
After a long and detailed cutscene, I was unleashed on the bridge of the Hyperion. I was able to talk with people, walk around the various areas to buy upgrades or mercs. The upgrades add a lot to the gameplay based on how you configure them. A good example was during the "rescue" mission, I decided to invest in the "strike turret" upgrade before heading over. It basically makes it so your bunker gets an automatic gun right on top of it, adding tons more firepower. I was able to create some choke points with those babies filled with marines, and slaughtered the zerg that came after me.
Every area of the Hyperion has a lot of character, from the armory with the head engineer and the lingering lackies, to the cantina in which you speak with the merc master filled with other troops and workers off-duty. It was here I noticed my first bug when the bartender lost his animations, and just stood motionless with his arms out. Still, the place looked great.
All the heads, even in the portraits, are perfectly lipsynced.
Really with the amount of choices and depth you have to pick your mission path, bonus missions, and well-done in game cutscenes, all I can say is I am more excited then I even was before going to BlizzCon.