Pros
Red Hat is working on some of the coolest stuff going on in open source like openStack. N if you are an OS guy RHEL is always the place to be. Very visionary senior management. I had the opportunity to listen to some of jim whitehurst talks, and I was convinced that he will take this company to places. very flexible work environment, overall a good place to be.
Cons
Not based on my personal experience, but from what I have heard, they are not a very good pay master. Red hat has a lot of workforce who works remotely, Now it does give a lot of flexibility to people who are looking for that kind of option, it sometime takes away the fun of working in person. This can sometimes make your life at red hat a bit secluded. Mentorship is hard to find in remote working model. Like all big companies it will boil down to which team you are working for, and who is your manager. RHEL is by far red hat most renowned product, and they are still not at par in other verticals, when it comes to their competitors. They are still trying to make a niche in their other business areas.