When it is written with conviction, ground in facts and avoids superlatives. Lay out exactly how it is, in a clear and easy to understand fashion. If you’re looking for references, go try and read quarterly reports from public companies. They are masters at presenting a lot of information in a clear, easy to understand fashion. You can even start by writing it in bullet points, then reworking it into a few paragraphs. This helps you start with the facts or series of statements that you want to get across.
This makes the executive summary, easy to read, understand. And then the recipient can dive in further. Which is what a good executive summary should do, invite them to go and explore further areas that might be relevant. That will help it stand out.
Using a tool like Hemingway App can be quite helpful in improving your writing. And to help it be crisp and clear.