The primary criticism about the NWT is that it introduces the name Jehovah in many places even though it is blatantly incorrect to do so. The other is changing the words to completely change the concepts of for example the trinity and heaven and hell, as well as the crucifixion.
It doesn’t take many words to change the meaning of a sentence. But the denial of Christ for example is very atypical in Bibles, Catholics and Protestants made very accurate translations even though it didn’t necessarily support their viewpoints, they would write the inconsistencies off to mythos, allegory etc.
JWs simply took their watchtower publication and used it to make a ‘More accurate translation’ instead of using it the other way around. They pretty much admit, that they believe this is a translation guided by God himself, as he would’ve intended it to be written (in their interpretation of course). I clearly remember in the 80s that they pretty much came out and said that all extant original texts were somehow modified and they somehow distilled the original wording. Although every religion has made a choice to leave out certain books completely from their canon, just like the JW did, the JW simply changed the Bible itself, even though many verses they cannot support the translation from any extant original text.