Pros
I really love it here. Fast-paced, interesting challenges, lots of trust and autonomy to put your ideas into reality and a really talented team who go the extra mile. The leadership balance this well with a culture of trust, nice perks and office atmosphere, and strong promotion of work-life balance. There's a real sense of everyone working hard towards a mission they really believe in. Lots of career advancement opportunities.
Cons
Basically just the flipsides of the pros of working in a startup - lots of change and lots of structure still to be implemented so you might need to carve out your own role (could be a pro or con!). You won't be able to coast but you'll be rewarded for what you put in.