There is a lot of replay value for Mass Effect 2, although most of it comes from importing different saves from Mass Effect 1. I don't personally know how well the short "interactive comic" thing will deliver on this, but I hope it will give enough choices to alter the story in a variety of different ways.
As far as gameplay goes, the game has 6 different classes for the player to choose from, so you essentially play through 6 times to beat it as every class. And trust me, the classes all play out very differently. I've beaten the game a good 9 times. Once as every class, with the Vanguard class and additional time and the Sentinel class another 2 times. I'm taking a break now before I go back and finish off playing as a Vanguard 1 more time and my Soldier class 1 more time.