The game came out when men were men and boys had 100's of hours to sink into each game. As such, the game is brutally unforgiving. I found that out when I lost the friggin' tutorial the first time I played it. Now I'm in the campaign, and it's kicking my butt. The first mission, I started over twice before I won the third time. The second mission, I lost 5 times in a row until finally winning the 6th time.
I still give it 5 stars as it's an excellent game, as you will see when you read the other reviews (which I agree with). Still, the difficulty is something I think needed to be brought to the forefront. If your frustration tolerance is low, the campaign may require the purchase of a new keyboard, as it is tempting to break it across your knee following yet another defeat. Having said that, the scenarios do have a difficulty setting.