Pros
Psyonix was started by a group of family and close friends who cared about quality and each other and that culture has continued on with a team that is now almost 40-people strong. As a relative newcomer, I have been nothing but pleased with how easy it has been to acclimate myself to the studio culture and how inviting and friendly my co-workers have been (in addition to their flexibility with personal schedules, which is highly appreciated when you have children at home). Crunch almost never happens (unless it's down-to-the-wire necessary) and the number of family/ spousal/ SO events that the company holds on a weekly (yes, weekly) basis is amazing. Plus, free food and drinks every day along with a very close proximity to the Gaslamp districts many, many, wonderful lunch places. On top of all that, the team really does care about making fun, high-quality games, which makes working here all the better. Psyonix really is that rare combination of both personal and professional satisfaction that you don't usually think are real.
Cons
Because the company isn't a large-size studio, you'll have to be ready to wear many hats -- some of which you weren't necessarily intended to do. There is also a lot of experimentation and prototyping here, which could be difficult for people who like to remained focused or refine one or two projects at a time.