Definitely not! I'm in my second year studying maths and I absolutely love it here. There is always something to do in Exeter - it's small enough to bump into people you know but still big enough so there is always something new to discover! Sure it may not be as big as some cities but there is a great selection of pubs, restaurants, night clubs and things to do. There are 11 clubs in Exeter the majority of them are really good fun especially since they are very student orientated!
About maths I love the course here. In my first year the course wasn't too intense, they give you a taste of all the areas of maths such as group theory, Newtonian Mechanics, computing etc. In your second year onwards you are allowed to take two "elective" credits outside of maths (I chose to take astrophysics and optics - some people I know have taken subjects ranging from Economics to Philosophy)!
If you'd like to know more about the course or university feel free to ask!