When you're using email as a marketing tool, you're working on a pretty personal basis. This isn't ‘drive-by' stuff -you're directly targeting customers from their inboxes. There's a huge amount of potential which comes with this kind of marketing... but you'll only reap that potential if you REALLY understand both the marketplace you're operating from, and the audience you're talking to.
The downside of just making offers is that they’re not useful on their own. People on your list won’t receive any value from you unless they buy what you’re promoting, so they have little reason to stay subscribed. That’s why this email marketing strategy doesn’t work alone. And it’s why many e-commerce sites struggle to keep people interested. There are a few exceptions (e.g., Groupon) that rely entirely on making offers—but then the reason people joined the list was specifically to receive those offers.
Alternatively, at least, an eye-catching design. It’s worth letting a proper designer have a go at prettifying your emails. Customers are often opening emails on the go, so you need to work hard to grab their attention. Making your emails nice to look at is a brilliant way to hold their eye. Netflix put time and effort into making their emails stand out, personally and visually – and it pays off for them!