i think a good addition to the game would be more diverse multiplayer modes. specifically more co-op modes. three basic ideas i have right off the bat are sieges, defense, and extirmination.
the siege type would be a team of players trying to break through the defenses of a force of AI enemies
defense would be the reverse, building up defenses and keeping out the AI invaders
extermination would put players in an area filled with enemies and split the players into fireteams. each team would clear out different areas. the team with the most kills wins.
