IF THEY HAVE first-person shooters in martial arts Valhalla, we’re pretty sure Tribes: Ascend is the one Bruce Lee plays. First and foremost, it’s a game about movement. In a split second, you have to judge where your jetpack-propelled, lightning-quick opponent is, where they’re going to be, and what you should do about it. You have to instinctively go with the flow, all the while never missing a beat. You must, well, be as water. Water with a jetpack.