Yes, Shepard is a pre-defined character. You can choose some personality aspects to Shepard as well as define what Shepard looks like, but I see that as a pre-defined character. It's not like in Skyrim, where the character is just a blank slate you can create into your own liking.

I'm in the camp that prefers my own crpg creations (as in TES games etc) mute.

I'm ok with a specific charcater (not my own creation) having a voice in principle, but in practice i find them too cliched and over-bearing to the point i often mod them out of the game (and rely on subtitles).

For my taste i found Morrowind about perfect in it's balance of voiced and written dialogue, where as Oblivion was far too focused on the voice to the point it made modding great mods for it more difficult.

Mute and Text please, with a smattering of varied and interesting NPC dialogue i can hear for the atmosphere of the game.

As said by others: silent protagonists are better for RPGs where you are supposed to BE the character and so hearing another person's voice might disassociate you from that character. But in games where you play a fixed character voice acting can enhance the experience like in Duke Nukem games where I am not the character of Duke but is simply a puppet master that pulls the strings of Duke and so I love the voice of Jon St. John.

I do generally speaking find voice acting to be overrated in games and I find music and ambient noises to be much more important for my gaming experience.

I just thought of an interesting case:

In Dragon Quest 3, ordinarily the main character (who is, perhaps, intended to be the player's avatar; this is espeically apparent in the remakes which start with a personality quiz much like Ultima 4-6) does not talk. However, there is one instance where, to enter a certain dungeon, one character needs to go in alone, and that character is always the first (living) character in the lineup. When you return from the dungeon, the rest of the party will be waiting, with the second party member at the front, and to leave, you have to talk to said second character. If that character is the protagonist, then the game will have the protagonist talk for one line. What do you think of this case?

(By the way, after beating the game you can remove the main character from the party. Try beating the game and see what happens during the ending!)

Indeed