What is more effective to promote new features on a website?

A client of ours wants us to highlight the new features of our redesign for his website. We think that we shouldn't explain too much, since it's a content-based website that hasn't had any drastic new features. It's pretty straightforward and our research has shown that the users know and understand the product pretty well. (Again it's content-based).

His idea to introduce this is by showing an overlay on top of the website, on first visit. The overlay has a carousel, showing all new features (5 of them).

How do I talk my client out of it? Or what is the best alternative tot tackle this problem on Desktop / Mobile ? Our idea was to use a one-pager as a last resort. (like https://www.youtube.com/new )