Changing the text "Add to Comment" in a given content type
You missed a key ['title'] in the array.

$build['links']['comment']['#links']['comment-add']['title'] = t('Add new review');


Make sure you follow the naming conventions while creating a custom module, or if you are doing it from theme replace the custom from custom_node_view_alter with the theme name (e.g. garland_node_view_alter for garland theme).

You can eliminate the extra check (for a while) of the content type for a while to check if the solution is working.