I have noticed the change in the “atmosphere” so to speak, when the mass is said ad orientem, even with both masses offered according to the Pauline missal.
I have especially noticed that the celebrant usually stops trying to “entertain” the congregation and tends to be more focused on the liturgical action.
I have never noticed this. I’ve been to both orientations, albeit I worship mainly in Benedictine monasteries. I’ve been to monasteries that do it in both directions. Frankly, to suggest that a monk-priest is trying to “entertain” the congregation is mildly offensive. Monks work hard to blend themselves into the liturgy. The Mass at our abbey is concelebrated, and the configuration of the altar, especially its positioning relative to the choir would have the perverse effect of causing the dropping of one Benedictine tradition to take on a specifically non-monastic one (ad orientem). Moreover, it would introduce a huge incongruity into the liturgy where the altar, and what happens on it, would be totally obscured by the concelebrating priests (roughly 15 plus some visiting priests on occasion).
To me that would detract from the reverence of the liturgy and detract from the communal aspect of the monastic liturgy.
That said, there was one parish where our schola regularly sang. The two regular priests there indeed tended to draw attention to themselves (especially with their homilies). At the consecration one liked to sing (rather loudly) the EP. The other didn’t really “put on a show” at that part of the liturgy.
However one day a visiting missionary priest filled in and like all religious, he was utterly transparent to the liturgy in that he carried it out with great humility and never imposing himself on it. He recited the Mass and did not sing, but did so with such reverence, humility and transparence that it was an utterly beautiful moment. He was the same during the homily, which was low-key, utterly orthodox and thoughtful.
To me it is setting up a false dichotomy to say that versus populum results in the priest trying to “entertain” the faithful (which he can nonetheless still do at the homily if he really leans that way).
And if a priest can be a distraction “versus populum”, what to say about this ad orientem Mass that I attended at Monte Cassino:
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It’s a far cry from the “noble simplicity” that Sacrosanctum Concilium called for (and not very keeping with the monastic tradition either). Note too that the monks’ stalls are behind the altar, so the abbot is actually versus populum for his community, which is keeping with monastic tradition. But the ostentation isn’t.