Biographical information on Mitchell can be found here and here. The Wikipedia entry on the 1980 Seville is here and a Hemmings article about a 1985 Seville is here.
Styling of the '80 Seville was controversial because Mitchell, enamored of circa-1940s "Razor Edge" coachwork on Rolls-Royces, slapped an interpretation of that style on the rear of a 1980 automobile. With mixed results, as we see below.
Seen from near the front, the Seville is a crisp design with some areas of ornamentation to provide interest. Not all Sevilles had two-color paint schemes, which were more of a 1940s and 50s fashion, but this is one of those rare cases where that practice enhanced the styling.
Here we get a better idea of its version of Razor Edge styling.
This shows the rear of the car from nearly end-on. I consider this the viewing angle where the design looks the most awkward. Seen in person, the styling makes the car appear a little too narrow and high by 1980 standards, even though the vehicle is generally fairly sleek.
There are many examples of English Razor Edge custom bodies. I offer this because of its similarity to the later Seville styling.