Graham Farish is synonymous with British outline N gauge (1:148), until recently a family run business, they are now part of Bachmann Industries Europe.
One of the first things Bachmann did was to introduce a new chassis to most of the diesel locomotives; this features a new motor and flywheel drive system which has proved to be a large improvement over the earlier models. Although work on new steam chassis will take longer to introduce, careful assembly and improved quality control have made huge strides to them in terms of smoother running.
What's it worth? Take a look at this Graham Farish price guide: sold listings for a value indication.