The game is great. Sound & graphics are awesome. I wish all the cinematics were HQ instead of realtime.
Challenge part is a great way to learn a bit more about the game units.
Achievements makes it a bit more fun.
Multiplayer is great too.
The fact that you can chat with people playing other blizzard game (wow for now) is great. I wish there was a way to play with or against anyone in the world. For example a friend in a different continent. Maybe some day we'll get there.
And I think the game was a bit short, considering the time people have been waiting for. Expansions are coming any way, but that means more money needs to be spent.
Overall is an awesome game.