I think that once the comparisons to other current cars of the time (late 70's through the late 80's) die away and a car is no longer seen against it's rivals of the it's time in the context of buying a new car, the deign reflects the spirit on the 70's rather than any particular ugliness/prettyness. My comments are aimed mainly for the Mk1 but also some of the things apply on the later cars.
Good points:
Big square bumpers (volvo tank style, well every car make needs an individual style quirkyness!)
Thinner window A and B pillars than modern cars (a good thing style/driving view wise, if not for strength!)
Thicker C pillar (in a very 70's style, in common with many (more) beautiful cars

)
Lots of metal in the front and back wings low down instead of crappy painted plastic bumpers (rust traps but just look better)
The early front is very distinctive with the square wrap around glass lens and stainless steel trim, but with a round headlamp reflector. The later headlights and separate indicators are less 300 and more 'general 80's' style (Mk 3 escort, Austin Ambassador, Mk 2 granada, Mk 2 fiesta...... ).
Nice shiny stainless steel (Mk only

)
RWD
I can see the bonnet from the drivers seat, always the sign of a proper car
Bad points:
High standard ride height (easily sorted)
Boat style comedy body roll (can at least improved with simple modifications, but if not, can give the appearance of speed at relatively low speeds, well it worked in the Sweeny anyway

)
Lacking in power (again can be sorted with a bit of work)
Was seen as a car driven by grannies with strong arms. (something only remembered by us over the hill oldies now anyway

so who's bothered)
Uglyness is in the eye of the beholder
As for the arse.......lowered, with wide wheels, fat tyres, a cloud of dust and the right camera angle, anything looks good! (even Jeremy Clarkson

)