I grew up in the Bulgarian Church (very little Bulgarian with the remainder in Church Slavonic). I understood and appreciated the services.
When we came to the States, it was disconcerting to realize that the congregants did not understand most of the service that was conducted in Church Slavonic and Bulgarian. I just did not sense that they were truly participating the the services.
I did not realize the enormity of the problem until (1) I read Father Alexander Schmemann's For the Life of the World and (b) attended an all English service at St. Innocent, Tarzana, California, and subsequently attended all English services at St. Herman in Littleton, Colorado. I now attend Holy Apostles in West Columbia, SC where all English also reigns.
I have attended other churches where services were not in English and it was my impression that the quality of the Divine Liturgy (the work of the laos) suffered as a result. Although it is hard to discern what people actually feel during services, the all English parishes practiced weekly communion of the entire congregation, nice attendance in Saturday (and Wednesday) Vespers, as well as feast days, and a true appreciation of the Faith. In contrast, at the parishes that used mainly non-English services, I saw nostalgia for and veneration of the non-English language (that bordered on cultic devotion) as well as a sense that the services being performed by the Priest, Deacon, chanters & choir was for their edification and enjoyment--may be similar to a traditional doctor-patient relationship. Frequent communion was out of question of course and the children and grandchildren dropped out and went elsewhere.
I have to say that another "epiphany" for me was hearing the "secret" prayers for the first time. What a wonderful and uplifting feeling to know that the entire laos, and not just those in the right side of the iconostasis, heard and associated with the very core of the Liturgy.
I will be the first to admit that services that are chanted or sang sound better when the music is congruent with the language. Perhaps more effort should be made to sacrifice the old tonal phrasings to accommodate the English text. My current church does a wonderful job of it and it is uplifting to hear the entire congregation and not just the choir singing almost the entire liturgy.