I played through several missions of Starcraft II: Wings of LIberty's campaign mode and a couple of versus matches (in which I got totally pwned of course) and performance-wise, everything runs great on my Personal Computer. I am able to play the game at 1920 x 1080 with all of the settings maxed out and the graphics engine is able to maintain a constant 30 frames per second even during hectic moments with a large amount of units on screen.
The textures option is a lie.
The game doesn't recommend the "Ultra" textures setting for my 9800GTX but switching back and forth between "High" and "Ultra" revealed no performance impact whatsoever - not to mention that the differences in the actual graphics quality are very subtle - so I just left that option to "Ultra". Visually, the actual gameplay section of the game is similar to how things looked in Warhammer 40,000: Dawn of War II, only slightly more polished so if you could run that game well, SCII should not be a problem for you. Blizzard is not known to be a developer that pushes graphics technology to its limit and the same goes here for the most part. The real time cinematic however is a completely different story - these sections of the game definitely qualify as some of the best looking graphics I have seen across all gaming platforms.
The gameplay section looks nice but some of the special effects failed to impress.
As much as it looks like one, this screenshot is not from a full motion video. It's all real time.