Vantaggi
In my experience (structured finance), staff quality of the european offices is very good, working atmosphere is fairly friendly and working hours are comparable to other BB Investment Banks. Leading position in Europe makes for interesting projects and A-list clients. Juniors are usually quickly involved in all aspects of transactions making a great place to learn.
Svantaggi
BNP Paribas' compensation packages are generally below market for junior and mid-level positions. Being a very large organization internal processes are fairly cumbersome and bureaucratic. Internal mobility level is low and career path can be slow (although with the after effects of the financial crisis it is probably true of many large corporate/investments banks. Management qualities are not really valued, resulting in average (sometimes poor) mid-level management.