I'm just gonna list things: small project scope down to earth accomplish-able goals. fun gameplay sweet stylized art direction no mandatory overtime good communication between team members little to no outsourcing
I'd love to work for sumo, especially as I live in the same city and I really like what they do but I'm sure they must outsource a lot of their art as they seem to have a really strong core team of 3d artists and don't seem to take on juniors at all...