Pros
Oxfam is trying to push the boundaries of what they can do within the funding restraints of a charity. This means you have to be innovative and that there's a lot of scope if you want to step outside your role and do more. The culture is good, relaxed, friendly and they recognise the importance of work/life balance. It's a very motivating place to be if you believe in the value the organisation are trying to contribute. The salary is certainly competitive but if your sole motivation is financial then this isn't the place for you.
Cons
Oxfam have the limitations you'd expect of a charity in terms of funding and a lot of ideas won't come to fruition because there isn't the money or resources to try everything. That said, this tends to mean more innovative work with what you do have. The second biggest con is that the organisation hasn't accepted digital fully at its core and the leadership in this field is left wanting. It's good but it's not leadership that will change the world.