2 things are bad:
1. Passport windows that constantly pop up - fixed
2. The fact that you get the same amount of cash no matter which mission you complete.
PS
Since I see that everybody is struggling with the 2nd scenario one advice: you can get that 1000 cash bonus, right? Add the fact that saving is only manual, so you can purchase a new unit, test it in battle and if you are not satisfied with its abilities reload the game and the save and check another unit. I assure you that you can build a squad that can get you through most of the missions. But I admit that you need to grind a bit to expand it beyond the initial 2 units - with only 2 of them you won't get very far. 5 units would be much better. The ending of second scenario is a bit hard and the finale of the 3rd scenario can stop you for a moment as well. 4th and 5th scenarios are surprisingly short and easy in comparison to the previous ones. I am currently stuck on 7th because the enemies seem to receive no damage or I am doing something wrong.
PS II
Ok, now I am a bit pissed, because my saved game got erased for no reason...