Pros
Interesting work, friendly atmosphere, nice staff - I think it depends on which office (and potentially which team within a larger office), but mine suits me very well. Directors are approachable too. (The lowish rating for career opportunities is purely a personal thing as I don't think I'll go much further - there are many people in the company who have started as engineers and moved up to associate, associate director and director - the opportunities are there)
Cons
The pension is the government minimum (2% company contribution within certain bands so actually less) - negotiate the other 3% on your salary if you're interviewing. Holiday is less than some of the big industries but ties in with other small companies. (The lowish rating for career opportunities is purely a personal thing - there are many people in the company who have started as engineers and moved up to associate, associate director and director -