Mass Effect 3's climactic campaign with some alterations. The galaxy's most important (and most imported) face is not being properly preserved in the transfer between some games of Mass Effect 2 and Mass Effect 3 (ours included), prompting BioWare to work on a correction.
According to BioWare's Community Coordinator, Chris Priestly, "The issue is likely in how faces were detected when imported from Mass Effect 1 into Mass Effect 2, and we're working on the best way to correct it for affected players." In our experience, a wonky import process only messes with facial data, and none of Shepard's recorded actions throughout the previous games.
If you're driven mad by inconsistent canon -- or can't bear the thought of Shepard being vain enough to get some touch-ups before his last stand -- BioWare is pointing you to a set of user-made tools for the PC version. As far as we know, this is the only time we'll ever recommend DIY facial surgery.