Vantaggi
Good Pay. Good Benefits. Some really excellent groups to work in on the technical side. Smart people in most cases. Some excellent technical management. Excellent training resources. Modern thinking generally.
Svantaggi
You roll the dice on getting competent management. Once someone makes Director level it's like tenure. You see many people who used to be competent and work hard get complacent once they hit Director level - it's like retirement with a job. Company values process over leadership. Challenging the status-quo is frowned upon. If you're not a subject of the crown or willing to move to London, you can forget that promotion. A less qualified Londoner will get it first. High-achievers, entrepreneurs are leaving for greener pastures, and average, non-challenging people are staying. Pulling more chips out of US and redistributing toward the Far East. (This is a "Pro" if you're in the Far East obviously)