Pros
In addition to awesome perks, catered meals, ping-pong, pool, outings, etc., they have more benefits than you'd expect from a Fortune 100 company. They consistently hire experts, who are also personable, considerate and truly care about the company and each other. It's fun. I've worked for 4 Fortune 100 companies and 3 previous startups. I've seen these companies struggle to create this culture, but to succeed it needs to come from the top where you must trade ego for involvement, lip-service for commitment and mediocrity for determination. Anyone can freely talk to the leadership staff anytime because they embody this culture. They call it being "an Elementum", but it's really just being a good person and doing the best job possible all the time. This startup is already succeeding and will continue to succeed for a number of reasons. But the main one is I don't see them doing any of the wrong things that caused the other ones to fail. This makes me more motivated to help in anyway possible to make it happen.
Cons
It's a startup! Schedules are tight and there's always too much work to do. You're always required to prioritize what's important to the company vs' yourself, and you sometimes need help figuring this out. However if you like heavy supervision, are not knowledgeable enough in your area, or are not self-driven to understand the bigger picture, than a startup might be the right place.