Pros
Great benefits and salary is reasonable for the area. Flexibility is nice especially if that's what you need in your life at the moment. Your job is generally very secure and safe and you have a lot of of wiggle room when it comes to performance and keeping your job. If you are looking for a long, stable career in one place with a lot of flexibility then Comcast might be a very good fit. Very much one of the few companies that I feel truly understands and does "diversity" right. Its not just a token effort but is very much ingrained in the culture.
Cons
Its a very large company so your personal experience can vary widely depending on your specific team and manager. If you are ambitious and looking to accomplish great things you will find a lot of cultural resistance. There is a tendency to do work for the sake of staying busy, and not to actually accomplish anything. A lot of groups are protective of their own processes/work and resistant to potentially positive changes. Management tends to treat every single project as the most critical which ultimately leads to a lack of trust - especially when internal products or project results are dropped within weeks of completion. Personally I have just completed my third project in a row where the finished product has gone ignored by the same stakeholders who were stating how vital the project was for the company's success. There is an overall lack of accountability when it comes to project success. Projects can slip in terms of budget and timeline by several months and hundreds of thousands of dollars and sponsors or project managers will simply move the goal posts. Very rare to have any revisiting of projects a year+ later to see if the business case has panned out or if returns have been met. No sense of lessons learned and mistakes are very often repeated. Be careful about promises of internal movement/promotion, especially across functions. Its possible to be able to advance through job openings on other teams, but it will be entirely on you to find these and pursue them. There is no sense in the broader company of an internal talent marketplace and often managers will look outside first - in my opinion this is due to lack of support from the talent acquisition teams. The Career Profile was advertised as a solution to this, but I have yet to hear about a success story where an individual was contacted by other groups within the company for opportunities or to work on new projects, or of any manager who used this tool when making a hiring decision. Your own resume, LinkedIn profile, and networking will do a lot more for your internal career growth than the Career Profile will.