Reviews are obviously a driving factor of ranking in Google My Business pack results. The prominence of reviews isn’t particularly shocking, as it’s a way for Google to crowdsource ranking factors, it’s hard to spam, and the most problematic type of abuse is illegal. It’s also something that let’s Google approximate online to offline ranking factors, as hot/trendy businesses are likely to skyrocket in terms of reviews before they are likely to kill it with traditional ranking factors. All of this means it’s something that is easier for them to trust then say, links.
At a high level, having a keyword you are trying to rank for, and a mention of a city you are working to rank in, in reviews has a high correlation with high ranking Google My Business results. Keep your eyes peeled as we have some exciting research in the pipeline to try to understand more about how Google uses reviews to rank businesses.
Another thing that seems to matter with Google My Business is engagement. Google clearly uses engagement to order search results, and local packs are no different. So, things like photos are content for your users to engage with. Same with reviews, which means they are likely valuable in several different ranking contexts.