Higher end Diesel engines are good units and yes have come a long way, run of the mill stuff, ford Peugeot etc the engines are poor, cheap, nasty and wouldn't be given one especially the 1.6 hdi that gets put in everything these days.
People think yes it's great on fuel it's saving me £££, no, you payed more for the car, the fuel is more expensive and you will never recoup that money as long as you own it especially when modern petrols do really good mpg anyway.
Then add in the costs due to driving a cheap pile, leaking injectors, cheap turbos, duel mass flywheels failing and over complicated electrics adding to the mess.