This is only true when the OT is interpreted in the context of the Talmud, which is a bad interpretation in my personal opinion. The OT actually has no doctrine at all, it is all about morality. The question is how to enforce this morality on members of our pathetic species. Moses did it basically by kicking butt. That works if you are in position of total power, which Moses was but most of us are not. The Pharisees/rabbis tried through legalism with rather mixed results. Jesus tried appealing to basic principles and largely failed. Paul turned Jesus into a god and made blind faith the starting point with the idea that morality can follow from faith. This also has had mixed results. But in fact the Christian Puritans probably did a better job following the morals of the OT than any other group did, so Christianity clearly has the potential to be completely compatible with the OT. On the other hand, modern Christianity is absolutely horrible and in total conflict with the OT. Orthodox Judaism is as blind as Christian faith, but replacing blind faith with blind legalism. It may be true that some mindless following is needed for most people.
From the perspective of the OT, doctrine is irrelevant. This is my view, so the question of finding common ground on doctrine means nothing to me. I like to discuss beliefs with others, but I don't care at all who agrees with my beliefs. What I do care about is moral action.
And moral action is seen in the practicing of Morality.