Okay so #42 has been guessed - Star Wars Rebel Assault II, by coolbeans - and #40 and #41 were already guessed sooner, so it's time for hints for two new games to keep it five games in front. I hope they're a bit harder and it'll take a few days but here goes;
#39: This game features campaigns for only five of the six civilisations, however, when you use cheats codes in a certain level, you can play a tiny secret level involving the missing civilisation.
#38: This game features three real life people but only one of them is on the cover.