Pros
Amazing perks: Friday breakfasts, catered meals, non-stop snacks, most of which were very healthy and included gluten-free, vegan, and vegetarian options. Fun is allowed, most obviously in the form of Nerf guns. Time-off policies were great because they trust employees to do great work, even when they aren't able to make it to the office. Everyone is friendly-- there are few people who wouldn't be willing to chat you up or hang out after work if the had the time. You are surrounded by really intelligent people.
Cons
Confusing leadership structure meant a lot of people were running fast and hard in a lot of directions without enough guidance to be as efficient as they could have been. It's typical in start-up culture that companies that grow quickly have a lot of growing pains and for some reason it's appealing to most people to not have a direct boss, but it often leads to a lot of confusion and wasted effort. There are not enough women. And that's not just a function of the talent pool-- women in the office are often slighted by the men. It's usually without any intention, but many of these guys are used to dismissing women or downplaying their talent and accomplishments, even on a subconscious level, and they aren't trying hard enough to FIX that. I think they've put priority on the product, obviously, but you don't build a good product without fully utilizing the great team you've put together and you can't do that if you keep shutting them down or making them feel out of place.