Pros
I can't say enough about the people that work at Twilio. It's an incredible team of hard working passionate people that embrace their coworkers. And they're a lot of fun: corn hole tournaments in the office, social work environment, dinners on Wednesday nights with fascinating speakers, and fun events of all types for foodies, techies, the outdoorsy, gamers and everything in between. There is also incredibly opportunity because of an incredible platform and relentless innovation. Management is very accessible and an incredible wealth of knowledge (especially Jeff Lawson and Bobby Napiltonia). Great training and on-boarding process (across departments) that welcomes you to the company, trains you with a great skill set, and familiarizes you with the people and product that make up the company.
Cons
You will be working hard and sometimes long hours, but it's well worth it. There are always processes that can be made more efficient (especially inter-departmental processes), but the company is always actively seeking to improve these.