You'll be better off playing Mass Effect 1 first, since it will be very hard to go back to it after ME2. The presentation and gameplay mechanics are superior in ME2 and after playing it, it will make ME1 seem like a giant step backwards. Not that ME1 is a bad game (far from it actually), it's just that ME2 improves on almost everything from ME1. Plus you'll appreciate the story more, including the consequences of your actions from the first game, once you import your ME1 character into ME2.