Mondeo's are good but it depends what stage of life you buy them in as above they do drive great etc however the weak point in the package is the TDCI engines. Sub 100K they tend to be ok turbo's don't last for some reason long after 100k ish the Delphi injectors fail and leak a lot, the water pump on them dies and the Dual Mass Flywheel also dies. All of the above are expensive to fix bar the W Pump and at the stage in the mondeo's life it almost makes it not worth repairing as its worth about £10.
For your average fleet buyer they are great for the first 3 years after that they are troublesome. It is also the same with any vehicle that uses the TDCI engine Jaguar X types, Transits etc.....
Ford aren't the only manufacturer to have issues with diesel engines mind. I wouldn't touch a BMW diesel especially 320D's or 330D's, the early VAG 140bhp 2.0ltr TDI, the Fiat diesels used in vauxhalls. Do a lot of research in diesels especially if you intend on keeping them for a long time reliability has been lost over the years trying to make them more refined and accountants making decisions over engineers.