Mass Effect 2 introduced me to the series and is the game that made it an absolutely unforgettable IP. The character development is about the best Ive ever seen in one game and it was a pleasure to experience. In Mass Effect 2, you really get to know and appreciate your comerades and it helps to motivate your progress throughout the game. The gameplay itself is hardly groundbreaking but it is a solid third person shooter with some fun added abilities at your disposal and an (albeit simplistic) leveling up system for a sense of progression. This game absolutely blew me away with an amazing mix of high level visuals and strong character interaction combined with solid gameplay and tight controls. The best action RPG on the system and one of a kind.
Note: I had a problem during one play through. There was some kind of loading error and my save file was corrupted and irretrevable. I dont know if this was a one off but Id recommend backing up your save on a USB every now and then.