The readers? The only thing that makes a translation great for them is whether the translated text reads well. Whether the translation is accurate to the source material is irrelevant; the readers literally can't tell and don't care, that's why they are reading a translation!
The publishers or whoever hired the translator(s)? The most important thing for them is speed of translation, how many words per minute. Accuracy and reading well are secondary to speed. Time is money.
The translators themselves? Depending on whether these are amateurs translating out of passion or professionals translating for a living, what makes a translation great is going to be either accuracy or speed (time is money!) respectively.
Personally, speaking as a Japanese-American who has done amateur translations (anime fansubs) at one point, being a translator is terrible; the absolute worst thing about it is that the work is thankless. Whoever reads your translations simply can't appreciate quality, and if you're translating for someone for hire there are usually more pressing concerns over quality.[1]
[1]: https://www.reddit.com/r/grandorder/comments/dnpzrh/everyone...