The RTS elements are revolutionary. PLAY IT ON BRUTAL or you won't appreciate the single player as much.
I recommend playing on Brutal so you really *understand* the advanced strategic style of this game. Each mission is a grind, but there is no confusion or tacky, archaic limitations that may frustrate. Whenever I fail, I know exactly why and I work to refine not just my strategy (which gives you a delicious variety of options), but my mental awareness and courage to meet the challenge and use hotkeys faster and more smoothly instead of becoming overwhelmed and just giving up.
This psychic factor, and the game's intensity, is what Blizzard focused on. This is what truly makes Starcraft II a next-generation title.
That way each time I beat a mission, it was far more rewarding, because I feel like I overcame something instead of amusing myself with some hand-holding cakewalk just so I could "see the story".
I understand some gamers play at a lower difficulty setting just to relax and experience the graphics, sound and lore of the game, and all the power to ya.
Personally I'm enjoying the story more because it is such a time-consuming challenge to get through each mission, it feels like an intense WAR instead of a silly game.
The game is so marvelously INTELLIGENT and I appreciate that its forcing my mind to work harder to crack the unique riddle each mission presents.
I haven't seen this kind of intelligence in gaming for a long time. I'm only talking about the SINGLE player experience, I'm staying away from multiplayer because I don't want to get addicted.
As of now, I'm only on the 11th mission or so on Brutal, but I'm savoring every moment of the game. I especially enjoyed the Zeratul & Kerrigan cinematic, that was unexpected and it blew me away.