I know that all you regular dopers excel at this sort of trivia, so I’ve come to you for aid. I think it was released sometime between 2003 and 2005. The basic idea was that you were piloting some kind of robot, somewhat humanoid in appearance (i.e. bipedal, two arm-like appendages) but with a very pronounced, angular, metallic look. Your goal was to destroy other similar-looking robots. I seem to remember that you could lock onto these enemies and fire missiles, lasers, etc.
Unfortunately, this is all I can remember right now. It’s a game that some of my old friends and I used to play, and I just remembered that it even existed. I went through the list of PS2 games (organized by release date) on GameSpot, but didn’t see anything that set off any bells.