“So first, we don’t want to make ‘Shepard 2′, or Mass Effect 4 with like, ‘oh there’s no more Shepard but you’re a soldier in the universe’. So this will be a very, very different context for sure, and nothing has been decided on the rest.” - BioWare Montreal producer Fabrice Condominas

In other words, get your fill of Shepard in Mass Effect 3. The series is moving on, but the commander isn't.