The one thing I don't like about Substack's design is the popup trying to get an email address. Its annoying to always have to click "let me read it first" instead of just being able to read the post.
Because of that particular dark pattern to trick people into giving Substack their email addresses, I wouldn't call their design unobtrusive but it is nonetheless still better than most of the modern web.
If they styled the "let me read first" to be more `democratic' (i.e. easier to scan for) I'd have 0 complaints. Maybe also as a button with an hr to separate it from the email form.
Because of that particular dark pattern to trick people into giving Substack their email addresses, I wouldn't call their design unobtrusive but it is nonetheless still better than most of the modern web.