Why would your first response be to write a letter?

Why would you not just sit down and ask our priest why he does or allows “this” or "that’ in the liturgy? You could make an appointment … take him to lunch, invite him to dinner, out for a cup of coffee …
Better yet would be to join the liturgy committee or the group that plans the liturgy for your parish

… before offering your “complaints” which may or may not be valid … you might get involved … be part of the solution or the process depending upon what insights you gain through your participation and study with this group …
Liturgy committees work in many of the areas that impact the liturgy: from training the ushers, EMHC, Lectors, and Altar servers to planning and/or approving the environmental elements. Ususally someone from the music ministry reports about the music to be focused on during the next liturgical cycle [ordinary, advent, lent, easter] …
Also, a representative from the RCIA team attends to coordinate those areas particular to the Rites for RCIA [Welcoming, Sending, Easter Vigil, etc] …
They review problems or areas of concern that occured during the liturgies including from parishioner complaints … even occassionally the "compliment’

…
They work on scheduling the “special Masses” like this Friday’s Feast of the Assumption …
Get involved, especially if you have knowledge and interest as noted by your sitting down to write a letter …
AND, personnally, I would never write this kind of correspondance in an email … bad form
