I just pre-ordered ME3, so am re-installing ME2 again while I wait until March 6. I played through ME2 at least half a dozen times. By choosing different team members and loadouts, the replayability factor is high. Both ME1 and 2 were fantastic games, so I am confiddent that ME3 will live up to my expectations... we shall see. One of the best games ever made was Dragon Age 1, but DA2 sucked pretty bad, do there is no guarantee.
Mass effect 2 sets the bar for storytelling in video game, and it's one of the strongest arguments that Video game is a form of art. I, for one, genuinely believe this game is a ground breaking game that beautifully combined shooter gameplay with a role playing storyline and it's also the best game Bioware offered so far after Baldur's Gate series. Die hard RPG fans may find this game a bit lacking, but the genre has to evolve to get better. Mass Effect 2 did it and did it brilliantly. First, the removal of redundant inventory makes mass effect 2 a very well paced game. Shepard can only carry several guns on mission and every weapon you start with is still viable in later game. Those changes are made for better experience. One thing I do miss is the weapon mods. they could do it like deus ex that gives a small and limited space to store some extra stuff. That's one of the reasons I can not give it a perfect 10. Second, character development is still a huge part of gameplay and the skills and abilities are still necessary for combat and social. Some people think that role-playing means running around for meaningless side quests (mass effect 1 comes to mind) and keeping track of stats. I would those are not what defines role playing game. Mass Effect 2 gives the player the true immersion that you can expect from a role playing story line. That means taking a role and feel your role not plodding with meaningless exploration and stats.