In a word: "smooth." Blizzard has clearly placed a lot of focus on making the unit control as natural and manageable as possible. The play style sits in a nice area between the original Starcraft and Warcraft III: it has the fast paced classic RTS style of Starcraft with the advanced control features of WC3. The game lives up to its hype.
Warcraft III control features present in Starcraft 2 include: autocasting, subgroup control, contextual rally pointing, building queuing, and Alt revealed unit health. A new feature that gives the game more of the Starcraft feel is the increased control group size--24 units can be added in a single group.
The game is also amazingly beautiful. If you are not a fan of the Blizzard art style, you may disagree, but for those of us who enjoy the bright, high contrast, colorful aesthetic present in their games, Starcraft 2 hits the mark. Units and buildings are easily distinguishable, preventing unit confusion even in novice players.
Two of the races are playable: Terran and Protoss (too bad for all the Zerg fans--myself included). The feel of both races remains rather true to the original game, with classic and completely new units working well together.
Check back tomorrow for an in depth look at the various units and structures available to Terran and Protoss.

View more screenshots on the
official Starcraft 2 site--TwiceUzi
One thing has not changed though: I suck at RTS. I already managed to lose the first map, with the Terrans on easy... I actually ran out of time as I got obsessed building all these new Terra units.