Nearly every intra-Christian argument since the Reformation runs through the sacraments, and the questions are specific rather than atmospheric.
How many. The Reformers reduced them to two, baptism and the Lord's Supper, on the ground that only those were instituted by Christ in scripture. Trent defined seven in 1547 with an anathema attached. The Orthodox perform the same seven and more besides, but have never fixed a number by any council they recognise, and Orthodox theologians themselves describe the count of seven as a borrowing from Latin scholasticism that entered their usage through seventeenth-century confessions.
What the Eucharist is. Catholic teaching holds that the substance of bread and wine becomes the body and blood of Christ while the appearances remain, a formulation using Aristotelian categories and defined at the Fourth Lateran Council in 1215. Lutherans affirm a real presence without that explanation. Reformed theology in Calvin's line holds a spiritual presence received by faith. Zwingli and most traditions downstream of him hold it to be a memorial. These positions are not compatible with one another, the differences produced executions in the sixteenth century, and they still prevent shared communion in the twenty-first.
Who may receive, and when. Infant baptism is standard in Catholic, Orthodox and most Protestant practice, and is rejected by Baptists, Anabaptists and Pentecostals in favour of baptism on profession of faith, which is why they baptise again adults who were baptised as infants, and why the word Anabaptist means re-baptiser and was originally an insult. Orthodox churches give communion to infants immediately after baptism; the Latin church waits until around the age of seven.
Each of these is a live disagreement between existing churches, held by people who can state the opposing case accurately, which is not true of every religious dispute.