Pros
You'll learn a tremendous amount about all aspects of IT. The analysts are terrific. The sales people are mostly professional and motivated. The staff across the company is great. Management...? See cons.
Cons
The robotic CEO and his C-level staff are all about metrics, many of which do not measure what is important to getting the job done or bringing sustainable growth to the company. Employee engagement is completely unimportant to the leader and his groupthink squad. Top analysts and sales pros are fleeing, and the CEO clearly feels that's fine: replace them with less-experienced people. It's all about the bureaucracy at Gartner (which is unwieldy as hell, by the way!). The culture feels more like the DMV than a profit-driven company. With only about 5,000 employees globally, that's just odd: I've seen plenty of companies with ten times that number of employees operate more smoothly than this.