Big shoes to fill, and it didn't fill them.
I'm going to target the veterans for the rest of this review since that is what I am myself. Immediately you get the feeling that SC2 is a stripped down version of the original SC that lacks the strategic depth that SC1 had. The biggest being that the economy and economic layer of the game is gone entirely.
There is no more adjacency bonus, storage systems or the possibility of a player starving their economy of resources. So buildings can be placed pretty much anywhere and even be used as cheap firebases since you can now add turrets and shields on them.. This truly feels like an arcade game rather than a strategy game in that pretty much the need for long term strategic planning is gone.
While you do have the new research tree it can be pretty much be unlocked within 10-15 minutes of playing and then it becomes a rush game. Experimentals can be pumped out almost as fast as regular units, while in SC it was a real accomplishment if an Experimental entered the field and it represented an investment of time and resouces that felt like it deserved to swing the battle in ones favor.
I'll leave the story and single player modes to the other reviews as I haven't gotten too far in it. But to summarize, the thing that's missing from SC2 is the strategic investment that one had to make in SC1. This is essentially an arcade game that can be good for a quick game, but for the large chess battles that were the hallmark of the original, one must go back to the original. (Which is not necessarily a bad thing in this case.)