I would say that the Mass (of which the Eucharist is the high point, IMHO) is the difference, and before I became Catholic, I did not understand this at all.
In my experience, the protestant services center on prayer, hymns, and the abilities of the person presiding over the service. The attention is principally on the man speaking and his words (even when he is speaking God’s words). The better the man (or woman) speaks, the greater the attendance because of the entertainment. The person has become the center of the church service. Again, my opinion only, and opinions like mileage may vary.
When I read how the early Church services were held, I looked around to see what churches were even using the same form. None of the protestant churches that I visited used it or anything comparable, and I visited many.
I visited a Catholic Mass with a friend, and was informed about abstaining from the Eucharist which, as a person with some Lutheran background (Mom’s side of the family, my attendance was rather nominal) was okay by me. It was very different than any protestant service I had ever attended. And many of the lies about Catholics that I had been told as I was growing up immediately evaporated into the ether.
The Mass, the Liturgy of the Word, and the Liturgy of the Eucharist, was entirely different than what I had experienced prior to that. The Mass was Bible centered, and Christ focused, wrapped in Holy Tradition and in the same form that the Early Church Fathers.
One might think that this nearly over-powering experience, this feeling of having arrived Home, would result in a near instant conversion, and it did…about two decades later (my fault, my fault, my grievous fault!).
I often wonder how different my life might have been like, had I listened to God’s call earlier in my life rather than late.
So, I understand your perspective, and respect your position for I once thought like you, that the Catholic Church was “just another denomination”…and now I know it’s not.
God bless you.