London Paddington: Brunel's busy diesel-stained masterpiece
London Waterloo: Too busy for my liking
Reading: Get on with it already!
Southend Victoria: The other Victorias are bigger
Thorpe Bay: Hello, my niece and cat!
Those are all the stations I use at least semi-regularly. Obviously some are not especially important, but all see upwards of 500,000 passengers a year and almost all see more than 1M a year. And some have too many visitors!