I live in Cambridge. In my opinion it's not particularly interesting as far as railways go - it's basically a diet of FCC 365s, Cross Country and NXEA 170s, NXEA EMUs and 153s to Ipswich. The station is very busy - according to Wikipedia it had nearly 7 million passengers last year. The main through platform is subdivided into two platforms with a diamond crossover half way. Therefore a London train can arrive and depart to King's Lynn whilst a NXEA Norwich train waits at the northern end. In addition there are two bay platforms at each end.
There's a lot of building work going on outside in conjunction with the new guided busway, which is due to open at the end of this month - at least the main part is, the section near the station may not be ready. If you're arriving at Cambridge from the south you'll see the guided busway being constructed along the trackbed of the old east - west route.
There are lots of sidings around the station area, they get full at weekends with FCC and NXEA units.
The branch to Bury St Edmunds used to cross all the sidings opposite the main platform, however this caused too many conflicting movements and it was relocated north to Coldham's Lane junction, with its sharp curves. My flat is near this and you can hear the trains squealing round twice an hour.
You could do a day return to Ely and visit the cathedral, visible from the station, or indeed walk into Cambridge town centre (about a mile). The town centre is good for shops, or you could take a look round one of the colleges.
For interest - as you walk out of Cambridge station, all the land there, stretching away for about half a mile in front of you, used to be railway sidings and sheds.
Look back onto the frontage of the station - there is the crest of each University college displayed.
Hope that's helpful.
