Hello @geronimo4j 
This query should do the trick, I first sorted all posts by date than I collected all ratings by Thing and only kept the first element in the list since it's the last rating then I returned ratings for all things:
MATCH (t:Thing)<-[:TAGGED]-(post:Post)<-[:WROTE]-(u:User { id: "abcdef"}), (post)-[:HAS_RATING]->(rating:Rating)
WITH t, post, rating
ORDER BY post.date DESC
WITH t, collect(rating)[0] AS rating
RETURN rating
Regards,
Cobra