Vantaggi
Your day-to-day peers, once you reach out/get to know them., are the highlight of Gartner. Throughout my time at Gartner I was able to partner with some of the most interesting and kind people. The benefits were also nice, good HSA health insurance and 401(k)--all available day one.
Svantaggi
Really consider where you want to go after Gartner. Within the IT space Gartner is a known name and the industry will have a good sense of what you do. Outside of that, the name is not marketable. Like another review said, this is not a place for people who like to be actionable. Client interaction is on-demand and it's highly probable you won't speak with them again. At the end, it will be difficult to articulate the impact you had, other than contributing to research. There is also a sense that Gartner is a place to wrap-up or park for the rest of your career. There are people with interesting experience, but the highly promoted researchers and analysts haven't worked in their respective industries for a while, making their ideas are flimsy and lack specificity. Other reviews mentioned this as well, but promotion and career pathing is very difficult. There are unsaid hurdles required to be cleared in order for promotion, and upon promotion the salary increase is minimal and consolidated with the annual cost-of-living increase every employee in good-standing receives.