Pros
Great place to work and learn. Smart colleagues, great in-team communication and direct management. You get to decide how to implement things, but you'll have to take responsibility for what you do. A lot of opportunities to grow by improving the code, the approach, etc. or owning the feature or project. If you like to constantly learn and improve - this place is for you. Nobody will force you to, but all the possibilities and conditions will be provided. Nice new office with good connections. Decent PCs. Latest technologies. Great work-life balance in addition to extra company events like company day, company breakfast, X-Mas party, sport events, poker tournaments and so on.
Cons
Some decisions are still taken from the start-up perspective - i.e. cutting corners and doing fast rather then right, but that goes away gradually.