Pros
The people around you are both smart and humble. Management are technical as well which is really good. There are nice benfits are in forms of good salaries, free snacks and drinks, many health benfits like free squash, yoga, runday etc.. Lastly, you are allowed to put quite a lot of time for self development. This has allowed me to improve myself that I think I would never have been able to at Google/Facebook/anywhere else. Even with all this, work life balance is really good. While companies like Facebook also has organized hackdays, they are far inferior since they are after work hours and only one day. Spotify have whole hackweeks once or twice a year. You can participate even if you don't want to stay at the office after work hours. I like the product myself and I feel that I'm fighting with the good guys (I wouldn't want to work with iTunes!).
Cons
Spotify is pretty bad at open source. It has a few successful projects though. But it could be much better imho. You don't always feel that non-tech people have caught the cultural vibe. I've been promised extra pension money and some small stock option at some point. Oddly I never got any of these benefits although applying for them. I also would like to have free food etc.. But these benefits are very rare in Stockholm. Not Spotify's fault, but housing is hard to find in Stockholm. Spotify's helps out a *lot* with this to be fair though.