h-review uses p-name, p-item, p-author, dt-published, p-rating, p-best, p-worst and e-content. h-review-aggregate summarizes many reviews with p-item, p-average, p-best, p-worst, p-count and p-votes (its spec is still a stub).
<div class="h-review"><a class="p-item h-item" href="https://microformats.org/">Microformats</a>
<data class="p-rating" value="5">5 stars</data> by <span class="p-author h-card">Joe Bloggs</span>
<p class="p-summary">The simplest way to publish structured data.</p></div>{"type": ["h-review"], "properties": {"item": [{"type": ["h-item"],
"properties": {"name": ["Microformats"], "url": ["https://microformats.org/"]},
"value": "Microformats"}], "rating": ["5"], "author": [{"type": ["h-card"],
"properties": {"name": ["Joe Bloggs"]}, "value": "Joe Bloggs"}],
"summary": ["The simplest way to publish structured data."]}}Google's rich results read only JSON-LD, Microdata and RDFa, so review stars in search need schema.org markup (Microformats vs JSON-LD).