I know we aren't focusing only on Cambs here, but I live in London, have lived in Cambridge and regularly cycle/commute in both.
Cambridge really isn't that expensive. There are tons of options on housing, the city is really easy for transportation, and most people don't have cars, and I don't only mean the students. It has a decent variety of things to do, though there is definitely a town vs gown thing going on. The pubs are really good. It is a minimum of 50 minutes from London King's Cross (they always quote 47 minutes on the timetables but this is BS), and about 80 minutes to London Liverpool Street.
As for density, I only find it's a bit packed in August when everyone and their monkey shows up to be tourists. Rest of the year is fine. Same thing with cycling. Most days it's A-OK, but during August or in the beginning of the uni term, watch out for those deadly confused cyclists.
There is a good variety of work for a small city and Stansted Airport is pretty decent.
However, if you are a city person, this is NOT a city.
C