Starcraft 2 is a pretty straightforward game: you know what you find, even before playing it.
Starcraft 2 is a, like I said in the title, pretty straightforward game. If you followed the series, if you read the previews, if you know Blizzard, you know very well what to expect from it. Anyone who is surprised, either positively or negatively, didn't really done his homework. Blizzard has never been a "revolutionary" company, but instead, "evolutionary". What it has always done is take the best features of what already exists, and refine the point of near perfection.
There is something drastically new in Starcraft 2 compared to the first? Keyword: drastic. Then no, nothing like that. But for those who follow Blizzard, it should not be surprising. There was nothing dramatically new in Warcraft 2 when you look at the first Warcraft (except, perhaps, the naval combat), the basics of the game remained the same. But at the same time, the game has enough new features to make the fans go through a completely new experience, even if somewhat nostalgic.
A comparison I like to use is with the Street Fighter series. For a casual gamer who does not delve into the game, the series has never changed. Ryu and Ken continue with their Hadoukens and Shoryukens. Six attack buttons, special moves... Apparently, the same game. And for most people, yes, one who had notions of how to play a SF will feel at home with newer versions. But for fans of the series, which deepens in it, each game brings profound changes to the mechanics. The same can be said about Starcraft 2. Superficially, it's the same game. But the center of any strategy game are its units, and in this respect, SC2 brings many news.
But all this you should already know. Starcraft 2 is a game that does not bother to follow trends, because Blizzard is a company mighty enough to follow their own ideas. As always, Blizzard is offering the best possible experience of a particular style of play: in the present case, an RTS with resource gathering and micromanaging. Do you expected a game like that since long ago? Then you'll love SC2. You're already bored with this style of game and want something completely different? So this is not a game for you.
But at what the game intends to do, Starcraft 2 does beautifully. Ah, and just one more thing: I didn't even comment about the custom maps that the community will make, in time. I can't even imagine how many games in one SC2 will be in the near future.
(And sorry for my bad english here, I'm a ESL.)