First of all I am sure that each game is a great game at what it does. I have not played Warhawk as I have a 360 and Halo is a great game single player and multiplayer. I think everyone should all be happy that we have great games to play on either system and everyone should stop flaming something that I'm sure most of you like myself have only played one or the other. I have seen the graphics on warhawk as well as Halo3 and they both have great graphics, not the best by any means for eith...
I have not played co-op yet but I did see in the game settings that you can change your network settings to allow only people on your friends list to join your co-op games which I believe is the default, however you can also make it so that it is open to anyone looking to play co-op. Check it out and see if this helps.