Hi there hyphenza , l truly loved and enjoyed your game ;)
regarding the content , I think with minimum effort you can implement several different companies with different coloring schemes and new or slightly altered bosses will make the game playable for couple of extra hours. With the available content (other than sandbox) I managed to finish the game under 2 hours. of course having extra story plots and new game mechanics (like stealth or something) will go a long way , but I understand that it isn't that easy >_<.