Gameplay looked like barely an alpha.
Re: cover-based gameplay. It had, indeed, shown up long before Gears of War. Dead to Rights and Manhunt are two other games that used that style of cover-based shooting. I'm sure that there were others before those. Rainbow Six: Vegas came out at the same time as Gears of War and its implementation of cover mechanics is a lot better. It's a shame that Gears of War gets all the credit for it, but that's how the gaming PR business works nowadays. I hope that Mass Effect does a better job of implementing it in the second game. At the very least, there should be a "take cover" button.
Double Agent was, indeed, a terrible game. The traffic light thing for whether or not you were visible was really dumb. I don't know what they were thinking there.