Is there an adjective meaning a more/less uneven aspect ratio?

Solution 1:

@BrianDonovan gave the very appropriate oblong, if you're looking for a word sounding more common, elongated also fits the purpose—it can mean something that "was made to be longer than wide", but also means "long in relation to width".

About oblong note that it seems to qualify only flat objects:

A rectangular object or flat figure with unequal adjacent sides

(Oxford dict.)

The word describing an aspect ratio close to one without completely prescribing the shape is rotund:

Approximately spherical; round, orbicular

(OED)

Solution 2:

The word is oblong:

longer in one direction than in the other direction (Merriam-Webster, first definition)

Solution 3:

The term aspect ratio is used in contexts other than imaging and displays. In aeronautics, for example, aspect ratio describes the ratio of the length of a wing to it's chord (width). In such circumstances it is quite common to describe a long, narrow wing (e.g. a sailplane) as having a high aspect ratio and a shorter or wider wing (e.g. the North American X-15) as having a low aspect ratio.

While this usage appears to be close to what you want to describe and is common terminology for people already familiar with aspect ratios in certain contexts, it may still require further explanation/definition if your target audience is not already familiar with the concept.