Avantages
I have been full-time at Unity for a few years now. Unity is a great place to work when it comes to working with some of the most talented people and getting the opportunities to actually make a difference in something big. It's also a great place to grow your career (but you need to know where to look for the opportunities to do so and how to do it). Work-life balance is generally good. Employees generally seem to be happy overall and the Copenhagen office is full of employees who are friends outside of the office. There is (from what I can tell) a lot of respect for the engineering team and it seems this far along the company is still (mostly) an engineering and product-based company. It seems like working at Unity becomes part of your identity, which is cool. The culture is not the same as it was a few years ago, but I think that they have done a good job of maintaining what they could when the company has grown to 500 people.
Inconvénients
Lack of software development experience/discipline from some senior people in R&D really shows when it comes to discipline and planning for R&D as a whole (this seems to be slowly getting better in some areas, but S...L...O...W...L...Y). Unity seems to have similar problems with planning and timeline as other big software organisations do (but they seem to be trying to take steps to improve the situation). Benefits for Copenhagen office don't seem so good for Denmark. The pay seems below average for software companies in Copenhagen and the compensation paid out during time off for paternity/maternity leave is quite bad, IMO, certainly not as good as what many other private companies in Copenhagen offer.