Many aspects of the game are hard and unrealistic (I mean Return Fire) but one seems unfairly easy.
When you see a Harvester heading straight at your base, you can quickly hire a bunch of rookies and buy some weapons too. Maybe buying weapons for immediate use is OK, but it seems unfair (to the aliens, but when were they fair to us you may ask) to get rookies and have then fighting for you 1 hour later.
How about a 24 hour "delivery" delay for soldiers? Maybe for all employees?