A good translation conveys the meaning of the original accurately and fluently in the target language.
Rather than cram the original concepts into the target language, optimum quality translations adapt the core message to the target audience. A free translation is not necessarily less accurate than a literal one.
The ultimate judges of quality are your readers, who should be able to read the translated text as effortlessly as those who read the original. Attaining that result is the ultimate benchmark of a successful translation.