Pros
The people: OUP hires so many hardworking, passionate, driven people. You will make great connections that last even when those people leave the company. OUP has a high employee turnover, so it's a great place to get that first publishing job. They have to replace people so often that it's a good place to find open positions. Turnover also causes a lot of assistants and coordinators to do work that is well above their job responsibilities. You will gain experience that can help you find a new job at a company that takes better care of their employees. Lots of happy hours since everyone quits!
Cons
OUP will teach you the hard lesson that the company you work for does not care about you. Your workload, work/life balance, mental health, career progression--none of that matters to senior management. Oxford will inevitably make you feel like you deserve to be mistreated, under payed, overworked. Be sure to leave before you start accepting the blatant corporate abuse that is tolerated in the office.