It was a decent experiment while it lasted. Google has announced that Review extensions will stop showing this month and will be deleted entirely in AdWords accounts in February.
An update appears on the support page about the extension. 
Advertisers that ran Review extensions and want to keep their historical data will need to export it in AdWords this month. That data can be found in both the new and old AdWords interfaces.
In the old interface:
And in the new interface (select the relevant date range):
It’s not all that surprising to see third-party Review extensions go by the wayside. They launched in 2013, but were never easy to get approved and as such, not widely implemented. The idea had been for businesses to be able to feature editorial quotes about their services in their ads, but that never really panned out. Even using the Better Business Bureau as a source became less of a guarantee of approval lately.
Hat tip: Steve Seeley
About The Author
As Third Door Media’s paid media reporter, Ginny Marvin writes about paid online marketing topics including paid search, paid social, display and retargeting for Search Engine Land and Marketing Land. With more than 15 years of marketing experience, Ginny has held both in-house and agency management positions. She provides search marketing and demand generation advice for ecommerce companies and can be found on Twitter as @ginnymarvin.