Marvel's Avengers was developed by Crystal Dynamics and Eidos Montreal with several veterans involved in the process. One of them was the creative director Shaun Escayg, who is of course the perhaps single most important person to the project.
That's why we suspect it is quite the blow that he has now left to get a new job. Or perhaps we should call it an old job, as he is once again back at Naughty Dog. Escayg was previously Director for Uncharted: The Lost Legacy, and we look forward to see what he will do next for his new/old employer.