Vantaggi
When I started working there, the firm was very entrepreneurial and grew from a scrappy upstart to a formidable competitor. The smaller size means a closer working relationship with senior colleagues and a better chance to learn more quickly. Not uncommon for top management to know the name of a graduate trainee and take an interest in that person's career development. Base salaries tend to be lower than other banks but bonuses are (were) generous if you perform well. There are a lot of top bankers that the firm has hired away from competitors and this presents a great opportunity to learn and grow in your career if you get to work with them.
Svantaggi
Aggressive atmosphere is encouraged by management, client-stealing and deal-grabbing happen frequently. If the person attempting to steal your clients/deals happens be senior to you, there is very little that you can do. Also, constant changes - some good, some bad. My manager/reporting lines changed more than once every year the entire time I was there - this was not unusual. Moving teams within the firm is extremely difficult - better to leave altogether, as any attempt to move to a different position will be viewed by your manager as an insult. They would rather see you leave the firm than have a possible negative reflection upon themselves. Therefore very important to know the team before you join - there are as many good teams in the firm as bad ones. Barclays Group presents a bit of bureaucracy to deal with, but Barcap is largely insulated from this.