Cameos:every non consequential character from ME shows up and reminds you of what you did for them. "Hey Shepard, remember me. You help me stop that Hanar from talking about the Enkindlers"
Fan Service: Tali's romance, every girl you helped in the first game wants to jump your bones in the second, dumb down mechanics, just keep in mind that BW listen's to it's fans a little to much.
The only thing that carried over was that Shepard was now the intergalactic James Bond (aka Captain Kirk) romancing every woman he encounters. ME3 will probably be a big intergalactic orgy, Shepard just running around and making out with different species :cross my fingers for a volus romantic interest: