Familiarity breeds contempt. Especially in video games. I know I might sound prejudiced, but off of the description you've given us, it sounds like StarCraft II isn't a spectacular feeling sequel game that most players like me have been hoping for.
This issue is certainly the bane of most sequels. However, it's really hard to say how it will apply with StarCraft. What they're doing is just very different from anything I've ever seen attempted before. They're making absolutely no attempt to change the core of the game. It's just StarCraft with a completely different set of tactics to use. People are pretty happy with how the original plays, and this is really just a graphical update with a new set of units that will hopefully keep people interested for another 10 years.
The only real revolutionary features in the game all have to do with battle.net, and all they're really doing is creating the community features that we've been wanting all along. The stuff like ladders and tournaments that other RTS games were never quite able to get perfect.