The Story and setting is what elevates this game and turns it into a masterpiece worthy of any classic Sci-Fi film though, the Story is just SO Epic! You play as well, anyone you want to be, you can change the characters gender, face, colour, name, personality and craft a character that really fits with you (you have the option of being a real Jerk, as displayed in this video http://youtu.be/xFajRU4xAVI or you can play as this really nice, sweet guy who cares for everyone. Other options include the stoic Hero, who sacrifices everything for the greater good or maybe even a mix of any two, or even of bit of all three! The game leaves the options up to you). I choose to be overly nice, but when the time comes a heart of complete stone. These options alone mean you'll have too play it for at least 100 times over to get every single miniscule amount of content in the Game. It doesn't stop with customising your character though, because thats just the start: EVERYTHING in this game can be changed, altered or reconstructed from the relationship you have with the Characters, Weapons, Skills, even shaping and modeling the Story!
Everything you do in the game will affect the endings outcome, heck if you've been a mean Bastard throughout the Game's entirety, the Game will reward you with all your Teamates dying at the end, and even YOU can die as well, ending the game completely: http://youtu.be/pRHhdc53Od8 or like me everyone could make it out alive: http://youtu.be/e-RFVPZhXbo . The coolest thing though is all the choices you made in Mass Effect 1 (sacrificing one character for another, one teamate dying in a arguement with another Team member ect...) can be IMPORTED into Mass Effect 2 so you can continue your 'arc' or 'journey' and then (reportedly the 1000+ decisions you would make over the past two games) that will be carried onto the final game Mass Effect 3 (its got this big Lord Of The Rings Trilogy thing going for it) and ALL OF THEM will shape the ultimate, ultimate ending. So the game can be played differently every time you play it then, which is just amazing! The fact that a programmed game can do this is just groundbreaking in terms of technology, giving you the impression that its 'your story'. Another, important thing you must do in the game is your Relationships with the other characters. And boy, there are tons of them, ranging from Assasins to Justicars, Robots to Merecenaries to Clones to, well every weird alien character there can be. Some provide comedic relief, others have some really F*cked up backrounds so theres plenty of diversity.
The fact that you'll like some more than others will also affect the Game, you can forge relationships over a period of time in the 30-80 Hours you will play ME2, with four optional love interests if you a play a man (http://youtu.be/oNixoKm9T7w , http://youtu.be/YLPk4pwmQ9Q , http://youtu.be/MP1gfoVQSyY , http://youtu.be/1Ja3EjKOqTU ) and three if you play a Woman ( http://youtu.be/ZinuVrgE7So , http://youtu.be/kFMdhHGKRZk , http://youtu.be/_9vMF7ooJes) *COUGH* Theirs even a...erm...Lesbian romance in there somewhere....better not show that..! So as you can see by now, Mass Effect 2 truly is as good as people are saying, and over the period of Days, Weeks (1 Week in my case) or Months that you play this game it will continue to evolve into something truly groundbreaking. This is a 'experience' unlike any other in a Game I've played, attaching you emotionally in a way that Movies or T.V never can. The interactability and diverse nature of this game DOES make it the best Game I've ever played and will definately pull on your heartstrings by the end. Just the fact that you get to be the main Character means its a experience worth searching for...