You can now review anything that has an entry on Wikidata, Wikimedia’s universal database of concepts. That means almost anything that has a Wikipedia entry, as well as lots of things that don’t — e.g., scientific papers, or individual episodes of webcomics. All you need to do is select the “Search Wikidata” function when starting a new review, like so:
We’re excluding some Wikimedia-specific stuff from the search results — if you get a “no relevant results” message, that’s why.
Of course, when you select a Wikidata item, you don’t have to manually add a label or description. They’ll be imported from Wikidata in all supported languages. In future we’ll import additional properties, as well, and keep them in sync with the Wikidata source.
This feature is brand new, and there are certainly going to be some issues with it. If you find one, please report it. :-)