One of the most addictive games I've ever played. It's just plain fun.
Pros:
The missions are great. They are the perfect length, starting out short and getting progressively longer. You can save your progress at any time and come back to it later, too.
The difficulty curve is just right. For people who are totally new to the genre, they have a fairly in depth training program to cover all the basics and a little bit of strategy.
Replay value is high. For most missions, you've got 3 unique commanding officers to choose from, but really, the game is so fun that I would play it again even if you only got to use 1. You also get ranked at the end of each mission, which makes you want to improve for next time.
The light-hearted presentation manages to be genuinely humorous at times. Even when it isn't particularly funny, it still doesn't detract from the game.
Cons:
To be honest, I can't really think of any. I suppose the story-line is a little weak, but the story isn't the point anyway.
Even if you've never played a turn-based strategy game before, do yourself a favor and pick up a copy. There is a reason this game gets ranked so highly by almost everyone.