I have not yet had the chande to play the SP campaign but from my experience with beta I can say: the game has a pretty steep learning curve. It took me almost 1 whole day at the beginning of the beta to win my first RTS fight (before that I was just loosing and loosing and loosing...)
Here are a few tips which maybe could help you:
- Familiarise yourself with units and their abilities. I think there is something like training grounds which maybe could be worth looking at before launching the campaign
- In the game setting there is the game speed option - maybe you could first try the lowest speed setting. The same is true for the AI difficulty.
- Use hotkeys rather than selecting with mouse (at least that is what I am doing)
And do not worry: Even I can now manage the RTS fights quite decently (although I have never really played an RTS game before)
