I'm going to start up this blog to share my experience with the Starcraft 2 beta. I'm 2-0 against other players and have tried out all three races against the computer AI (only "very easy" available right now).
Orbital Station (upgraded Command Center) has an ability called "Call down supplies" which is very handy, especially because I keep forgetting to keep my supply high enough.
Siege tanks work a lot better for uphill sieging as they no longer have a chance to miss when shooting at something on higher group (you just need to have sight on the target).
Marauders are very nice and give Terran a handy anti-mech unit.
The Nexus has the new Protoss macro ability "Chrono boost" which speeds up a building's production or researching for 30 seconds. It costs 25 out of the Nexus's 100 mana and might very well be overpowered. It is extremely useful for boosting probe production, pumping out Colossi a bit faster, and pretty much anything that involves training or researching.
Void rays are really useful. I took out the Planetary Fortress in a Terran player's expansion in about 5 seconds using 3 void rays. Their charging up attacks make quick work of buildings as well as Thor, as I discovered.
The Gateway's ability to switch to a Warp Gate and warp in units anywhere on the map within the psionic matrix is also very cool and helps for reinforcing attacks on the enemy base.
The new and more important queen is a nice touch to the Zerg feel. She can lay creep tumors (which are how the creep is extended now), spawn more larva at a hatchery, and heal a friendly unit.
Nydus worms combined with the Overlord's new ability to spawn creep greatly improve Zerg mobility, allowing instant transportation across the map.
The distinct waypoints at the hatchery for drones vs other units threw me off at first until I realize that I could also set waypoints for morphing larva directly.
I'm going to try to record some of my games and put them on YouTube, so if anyone has any special requests, let me know.