If you liked Starcraft at all then you will fall in love with this one...
Starcraft II takes place about four years after the original. WoL focuses specifically on the Terrans (Humans) for the single-player campaign, but allows you full access to all three races for multiplayer.
The campaign consists of 26 missions, many of which you can do in a non-linear tree. Each mission unlocks new units, research options, and awards credits. Research allows upgrades to units and buildings in an either/or fashion. An example being, do you want to have units start with +100 energy or have your buildings slowly heal themselves? Credits are spent on mercenaries as well as upgrades to buildings and units. Since there are a limited amount of research options and credits, you will be forced to not get every upgrade. This encourages you to play more to your style or try playing through the campaign again to try different combinations.
After you finish the campaign there are a number of other modes you can try including challenges, co-op missions, custom games, and standard multiplayer. Challenges are a nice twist, especially for the achievement hungry. Co-op is pretty self-explanatory, teaming players against AI on maps of your choosing. Custom games are usually tweaked rules matches from user made maps, such as a tower defense or an RPG style map. Multiplayer can be anything from 1vs1 to 4vs4 as well as FFA of course. Every mode feels polished and slick in presentation and has plenty of achievements to unlock.
The achievement system awards points for each unlocked, with the more difficult ones giving more points. These points are displayed next to your portrait almost like a gamerscore or trophy level. New portraits can be unlocked by gaining new achievements as well, making the achievement system very addictive for those who are interested, while being completely optional for those who aren't.
All in all, Starcraft II delivers the same type of deep story, polished gameplay, and balanced multiplayer you've come to expect from Blizzard. If you have a Mac or PC that can run this game, you owe it to yourself to at least give it a try... Find a friend who bought the game and get a Guest Pass to try it out!