I have a mk3 diesel clio.
I cannot comment on the comparison to older clios, but the built quality is excellent and I am getting 50mpg for day to day journeys.
It has some power even in 5th, so you always have acceleration, in fact anything over 45 mph just leave it in 5th.
In my car, theres a few things missing that I'd like that didnt come, like climate control, cruise control., but overall it is a very solid car.
Won car of the year 2006 aparently
5 star euro n-cap.
They are pricey really, and it wasnt my first choice of car, but I'm happy with it. If you wanna know any more feel free to ask.