Vantaggi
Good people, competitive salary, improving corporate culture, many opportunities for further career growth. I can only speak for my limited view of the company when I write this, but the word on the street often gives Santander a bad reputation in terms of being a desirable place to work. My exposure so far sees this view as unwarranted or out-of-date.
Svantaggi
It is a big, international bank and comes with many of the challenges facing companies of this size. There's a lot of red tape, processes, and inefficiency. It does seem that the company is taking on many of these challenges but there needs to be a continued commitment for improvements to continue. If you've worked in a big bank before, none of these challenges will be new or surprising to you. If you are used to small companies that can move quickly and desire a work environment like that, then this is not your best fit.