They teach righteousness through works, whereas the Apostle Paul stated otherwise.
The Bible clearly states that Deborah was a judge, WT contradicts the Bible.
They claim that the NT is inspired by God, but when the verse 'All scripture is inspired by God' was written, the NT didn't even exist yet.
They never delve into the cultural meaning of NT rules, like about women covering their heads etc, there was a direct cultural reason for this that they are clueless about, among other teachings of Jesus like turning the other cheek, walking an extra mile, givithe inner cloak. These teachings make no sense unless the cultural norms of the 1st century are known.
WT does no real research.