I recall this series fondly however I don't remember seeing the pilot nor the last 1-hr retrospect episode. I do remember looking forward to each week's show, my wife and pre-teen daughter would enjoy watching it, a few times we had friends over who also liked it.
The leader of the prisoners was a Puerto Rican dude named Fuentes played by Jose Perez, he not only was very funny but typical of mid-70s TV, the character Fuentes was not afraid to make social commentary. I also liked the lead Black prisoner DeMott as portrayed by Hal Williams who was frequently seen on Sanford & Son playing Officer Smitty. The popular character actor of the 70s Rick Hurst was hilarious as inmate Cleaver and the veteran Mel Stewart(George Jefferson's brother Hnery on All in the Family). The dissapointing role was by frequent game show panelist, Tom Poston as Guard Sullivan, he was goofy and just was not believable.
Like other sitcoms of the period, On The Rocks was based on a Britsh TV show, in this case, "Porridge". This series may not have been the best nor the funniest of the 1975-'76 season but it was superior to many others who were renewed for another season or two. The cancellation was due to lack of sponsor support as it was considered too benign a view of prison life so few were willing to buy ad time, this was furthered by letters to the network by members of the penal system frowning on its portrayal of life behind bars.
I look forward to the day that the entire series is eventually released on a DVD box set.