I never played the first one, so I didn't have as much to base an opion of as you did. I enjoyed it for the most part. Could care less about story, and usually have the tv on mute when I play it. An overall fun arcade style shooter.
Only thing that really got to me was the amount of friendly fire I had to put up with. Don't tell me they didn't pick up on that in the testing phase. If my dickwad AI teammates can't go 60 seconds without putting a bullet (or more than likely rocket) in my back, turn friendly fire OFF.