Pros
Gainsight changed my outlook on work. This sounds dramatic, but I spent several years in fast-growth SaaS where politics and jerks were rewarded, and the executive team (and every iteration of it) helped me see and recognize that incredible human beings could make great leaders as well and win in business. Gainsight was an MBA in SaaS and leadership - you get to work with the very brightest and the bar is exceptionally high from your customers as THE Customer Success company. Product is the best in the market. The only success of competitors is copying the playbook and being cheaper since they don't have to pave any new trails. If you are serious about CS and your career, customers are very happy and incredibly successful. Benefits are amazing, even recharge days (which as a PS leader was tricky!) and the indoctrination (in a very good way) in Human-First leadership will transform you as a leader and teammate. Access to leadership is unparalleled (CFO doing weekly office hours anyone can dial in, frequent touch points with CEO/Exec team) with a high level of authentic transparency.
Cons
Prior to Gainsight, I was used to being the smartest person in the room OR working really hard to stand out. At Gainsight, that is table stakes, so brilliant people work very hard to get a spotlight. This also leads to attracting incredible talent who can't all get promotions at every opportunity (ie for every manager role there are 4 people ready and capable internally.)