Silent Let's plays are called Walkthroughs I think.
But yes you can try it out, hell I even do this when I'm uploading my replay solutions to level packs and I've been doing this for years now
If you want to express your thoughts about levels I would certainly encourage you to ditch subtitles and pick up your microphone instead. Text covers up the action, the viewer needs to read rather than watch....
If you are unsecure about your voice or anything, there's ne need to be.
So if you want to tell the viewers something it's better to use your voice rather than text. If you just want to show stuff, the game audio can be enough.