I don't think it would be fair of me to criticize the styling of the new models because the mid-1970s were difficult times for Detroit's engineering and styling staffs, though I couldn't quite resist the temptation, as you will see below. Some of the difficulties have to do with the car market, because buyers shifted to smaller, usually imported cars with better fuel consumption than the large, traditional American automobiles that dominated the market when the gasoline crisis hit. Most of the difficulties were related to government regulations related to engine emissions, passenger safety and crash worthiness, the latter having to do with stronger bumpers being mandated.
One way to improve fuel economy is weight reduction. At the time when the new '78s were conceived (1974 or thereabouts), production models tended to be long, with plenty of rear overhang. So the 1978 redesign had the wheelbase reduced about 8 inches (20 cm) and overall length shortened as much as 17 inches (35 cm) for Buick models. Most of these reductions were applied to the rear of the cars, creating what seemed at the time to be a stubby or 'bob-tailed" look.
The 1970s were a time when Mercedes-Benz styling was influential in Detroit, so the new A-platform cars and many others had a crisp appearance based on what was called the "three box" configuration (the general shape resembling two boxes placed end-to-end with a box centered on top). In any case, GM's styling supremo Bill Mitchell had a preference for sharply creased edges and transitions, so the new designs must have met his approval.
This is a four-door version by Pontiac. Note the attempt at a "flowing" fender line with a rear apex at the C-pillar, this to distinguish Pontiacs from other makes sharing the platform.
Two-door and four-door A-platform Buicks are shown here. Rear side window glass on the 2-door models did not roll down, a source of customer dissatisfaction and probably lost sales. Unlike A-platform Chevrolets and Pontiacs, the Buick and Oldsmobile versions were given "fastback" rather than "notchback" or "bustleback" styling. Although the styling effort might have been well-intended, the result emphasized the fact that the cars' rears had been chopped off compared to previous models.
This is the Oldsmobile version.