UCL is a great university and top-notch research institution in Belgium, by all means equivalent (if not superior in my field) to KU Leuven and all other universities in the neighbourhood. I have been treated in an excellent fashion as a scientist. The workplace is open and it is very easy to fit in on the personal and professional side.
Great environment and scientific relevance.
No additional benefits (but salary for scientists is relatively high), scientist posts are intrinsically precarious and short-term.