After reading a few reviews prior to purchasing the game, I was expecting to play SC1 but with better graphics and higher resolutions. Well, yeah.. it pretty much is. I don't want to repeat what you could read in other professional reviews, so I'll keep it short. Is SC2 worth buying?
If you are like me and enjoy hardcore PvP on casual terms, then yes SC2 is definitely worth buying. They've made PvP convenient and awesome! There is a 'Quick Game' button that launches you into a PvP 1v1 match against someone of 'equal' skill. I honestly couldn't design a casual PvP game better than that. Click, boom your in! Pow, pow! Awesome!
At my level (very noob), your average game goes for about 35 minutes, which is perfect for slotting into those free time gaps. I can see this becoming the TF2 of RTS.
As another positive, it's very easy to play with friends and there are achievements and unlocks that you can showcase for your e-peen. The single player campaign is pretty good too. They also have challenge missions that are like playing mods from SC1. For example: Defeat 3 waves of enemies with limited units. You buy the most awesome RTS ever made and get a bunch of free mini games... can't complain.
I spent the entire weekend playing it and I want to keep playing it. Starcraft 2 was definitely worth the money I paid, and then some. Love it!