Vantaggi
Your colleagues tend to be incredibly smart people, the work is interesting and you get a definite sense that it'll have a meaningful impact on the world. Consequently, the company treats you extremely well - it held a global conference for graduates recently with all recent graduates from around the world meeting up, which was fun and informative. You're also expected to be proactive and think about ways to innovate in everything you do. Senior management are very friendly and approachable and do keep an eye on everything that's going on. Our division's GM in particular was well-known for going around the office personally to hear from the engineers and collect their feedback. You also get a distinct sense that it's genuinely run by engineers rather than the traditional business types. A lot of sales and marketing people were originally engineers, one of the lawyers was a software engineer who then retrained, and a lot of the C-suite (including the CEO) also have engineering backgrounds. It makes a big difference to the culture of the company; while it's raking in plenty of profit, you never feel that they're single-mindedly focused on chasing profits and satisfying shareholders.
Svantaggi
Bureaucracy has increased somewhat as a consequence of becoming a large company. Still better than other companies in the same industry and of similar size though. Pay is not the best in the industry, but for me this is easily made up by the other benefits (RSUs, cash bonus, private health/travel insurance, pension scheme), the work/life balance and flexibility, and the fact that working at ARM will improve your future career prospects. Most importantly, you won't have to live in London!