There are a lot of ways to judge print quality. Start with accuracy which is mostly an indicator of printer calibration. Do parts come out the intended size and shape? Are circles actually circular? Are right angle actually right angles?
Then you look at finish which is mostly a matter of precision.
If it's ABS, especially if it's large, you look for delamination or warping.
If it was printed with support material, did it come of cleanly or cause some surface damage?
You can also consider things like strength and suitability for the intended purpose, but both are pretty hard to judge based on a picture.
The print quality tells only part of the story with regard to the printer. Almost any piece of junk will turn out a decent print once in a while, but a good printer should deliver quality prints reliably, and without a lot of extra work to make it do so. Some of that is hard to separate from the skill of the operator. Even a good machine can turn out bad prints if the operstor doesn't know how to use it.
