They do their best to make the game accessible to casual and new-to-RTS players, with hands-on and video tutorials, a tips system, etc. They also have a casual difficulty level in the campaign to get your feet wet before going on to normal, hard, and brutal diffs.
The gameplay mechanics haven't changed much since the original Starcraft though, but it's prettier now and the storyline's more immersive with in-engine cutscenes and a lot of interactive content. If you're not much of a RTS fan, it may be worth waiting for the price to drop a little... I'm not sure it's worth full retail price if you're on the fence.
So pros and cons. But I don't have regrets getting it on launch day.
Myst was awesome too though!