Same idea/engine? Crackdown is using an engine called RenderWare. There is a list on Wikipedia with some games using this engine:
http://en.wikipedia.org/wiki/RenderWare.
About the idea, is it a GTA type of game? Does it take place in an open world? Can you use weapons and driving vehicles? What game play mechanisms is similar/same except from the headquarters thing? I actually started a website (
www.gtaclone.com) about GTA type games, aka GTA clones. If this is such a game, there is a big chance it's listed on my site :)
www.gtaclone.com