Pros
The work-life balance is excellent and so is the pay. For me as a translator, it was a very interesting professional challenge for the first few years. Lots of opportunities for learning additional languages and taking part in other training, you definitely can learn a lot. The department I worked in generally had good working culture, the atmosphere was very friendly, lot of open-minded people who enjoyed working together and helping eachother - it was probably the best aspect of the job beside the very interesting multicultural environment that's generally present everywhere in the Commission.
Cons
When I was working there, the workload was high but manageable, but from what I hear, it's getting worse every year. Also, once you get used to the type of documents to translate, it quickly becomes very repetitive and frustrating for anyone who needs some variety and creativity to function properly. The procedures are rigid and often bureaucratic and you sometimes have to deal with micromanagers who want to have every single detail under control, but can't put together the bigger picture, thus wasting their own and everyone else's time. As far as career mobility is concerned, translators have long had the reputation of the most frustrated caste of all EC employees: the ones who most frequently request mobility and least frequently manage to move somewhere else in the service.