Curiously difficult question for me to answer. Maybe I'm not reflective enough.
But among the surprises to me were finding that Charles Taze Russell believed 1) that there are historical mistakes in the Bible 2) that animals may have evolved into their different species rather than being direct creations 3) that Jesus is to be worshipped 4) that many forerunners of the Bible Students were genuine Christians and 5) that all, or most humans will be saved by God in the end.
All of which are pretty good ideas that JWs would do well to revisit, in my view.