It's a very borad question, so I'll try and answer this briefly. As with anything, one persons experiences and opinions aren't shared by everyone, so this is just my view of it!
Re: Small TownCanterbury is classified as a city (the cathedral seals that deal) but in reality it's just a town - not an especially large one, but the residential areas sprawled out making it slightly bigger than most realise. A large proportion of the residents there consist of students. There's Uni of Kent, Canterbury Christchurch Uni (booo) and a branch of the University for Creative Arts all packed into a relatively small area. Lots of young people but of course a fair proportion of locals and in warmer months, lots of tourists(!) passing through on their to London.
Nightlife - I've made a thread here, check it out. I desperately need to update it but now I'm no longer at Kent it feels like more of a chore.
http://www.thestudentroom.co.uk/showthread.php?t=2412590Shops - Typical high street shops, depends really what you're after. Typical shops for the typical young person. If you're really curious, a bunch are centered in town around an area known as Whitefriars by the bus station. Shops are listed on there
http://www.whitefriars-canterbury.co.uk/ Plenty of other shops around too, not just limited to what you see there. Jack Wills and Primark have also set up in Canters due to the high number of students. Supermarkets are dotted around, with a Tesco Express bang in the centre and anything you might need electrical as student can be found in some of the retail parks a short bus ride out
Cinema - Yup, there's an Odeon. A minutes walk from the bus station in town, next to Chill nightclub. Four or five screens - screen 1 has a huge amount of seating but it does mean it can get a bit chilly in such a cavernous space.
Expensive - Much like the rest of the south east, it's not going to be cheap. Having said that, housing prices for student lets are fairly competitive and aren't wildly different from other uni towns in the south. As I say, lots of students therefore a big market for cheaper housing. If you're used to the north, then pubs and clubs will seem eye-wateringly expensive but again there are plenty of student deals and campus is competitively priced when taking the south as whole into account.
How big is it?Feel like I've been over it really. Have a gander on Google Maps and compare it to your home time might give you a good idea?
Feel free to fire any more questions