Good company, interesting work, nice peopleThe good thingsLots of freedom. Good management style, they give you tasks and let you just get on with them - no standing over you and asking you what you do each day.
Good team spirit.
Lots of nice, smart people.
Flexi time is very useful - good for when I have to drop my kids off at school some mornings.
The challengesYou get to do a lot of different tasks - some people may find this challenging.
There is not a lot of after hours bonding - most people come to work and don't mix socially after hours. Most people seem to like this as there is good work life separation - some people may prefer a work environment that is more social.