Pros
A job you can probably do in your sleep, unless your manager decides it's time to enforce arbitrary targets. Interesting for the first year, then you run out of things to learn and they will try to keep you busy with completely pointless projects that absolutely no one will ever look at again after you finish them. If you want an easy job with an average paycheck, this is the place for you. (You can WFH full time!) There are some really great people working at the company, so if you're lucky you'll make friends. Gartner is a safe place to land, no layoffs in sight, company will continue to grow no matter the economic uncertainty.
Cons
Pay is below market, and with inflation doing what it is and the company only giving what they call "merit" increases every year, you will basically take a pay cut every April. Competitors in London will pay 10-30k more for the same role. Career advancement is pushed as the big reason to come to Gartner and stay. The idea is that since they pay below market, the learning opportunities and brand should keep you engaged. This does not work long term as you run out of things to learn fairly quickly and promotions are far and few between. If you do get promoted, increases are so minimal, it's almost not worth the extra work you're taking on.