Vantaggi
ServiceNow employees tend to be passionate about what they do. I work in development, and it's a fast paced and challenging environment for me. The nature of the product means that there are always problems to solve at scale for the customer base. The upper management team, as far as I've interacted with them, are top notch people in the field. I would not describe them as typical managers, or rather as the kind of people that you would see in Dilbert cartoons. Additionally, I'll note that compared to other companies I've seen, ServiceNow tends to promote from within. I myself have been promoted in lieu of bringing in a new person on a couple of occasions. It has allowed me to grow with the company.
Svantaggi
If you just want a job to get paid, then ServiceNow may not be the right fit for you. At least in development where I am, the most successful people here are ones that care about what they do and want to build a compelling piece of technology.