Also, and this was really good, celebration versus populum requires a great deal more concentration and focus for the priest, more focus than many priests have. Forgetting a proper ars celebrandi they become "priest showman" as if they were on TV. They become the focus of the action, not the Lord.I think another detriment of versus populum is that, in addition to the priest becoming the center of attention, the priest has more of an opportunity to make the congregation feel like they are the center of attention. I am referring particularly to the habit some priests have of sweeping their eyes across the congregation, while praying to the Father on their behalf.
Or another example: after the Eucharistic Prayer, when our Lord Jesus Christ is present in the Blessed Sacrament on the altar, the priest says: "Lord Jesus Christ, you said to your apostles: I leave you peace, my peace I give you. Look not on our sins, but on the faith of your Church, and grant us the peace and unity of your kingdom where you live for ever and ever." Unless I'm mistaken, the rubrics for the Extraordinary Form instruct the priest to gaze upon Jesus Christ present in the Blessed Sacrament, since he is addressing our Lord with these words. Nowadays, the priest is usually looking anywhere but the altar, trying to make eye contact with every member of the congregation. The example the Holy Father has set—placing the crucifix upon the altar, facing him—is something that might help priests remember on whom the focus of Mass should be.