A lot of the original reviews are dated for the 2013 release of the first OVA-single, which appropriately reflect that. However, it's important to note that since 2013 and after the airing of season 2, this same listing was updated to also capture the Kako-hen OVA releases (essentially OVA 2-6). The Kako-hen OVA essentially concludes the animation and could be considered a short S3.
Although the execution had its faults (being a bit rushed), these OVAs are definitely a must watch if you enjoyed S2 and felt that the state of relationships lacked closure.
I recommend watching S1 -> OVA 1 -> S2 -> OVA 2-6