As the title suggests this is a side story to the 2011 series 'Puella Magi Madoka Magica'; these comments assume you have seen that series but won't include any spoilers for it. This series is centred on Iroha Tamaki, a girl who has somehow forgotten the wish she made before becoming a magical girl. After meeting a small Kyubey she recalls that she healed her sister Ui... who is now missing. Hoping to find her she heads to Kamihama City where she meets many other magical girls. They are congregating there as they have heard a rumour that magical girls may be released from their duties there. Inevitably they find themselves battling several witches.
I wouldn't say this is a bad series but it doesn't stand up to the original. There are no major surprises and the sense of danger was somewhat lower. The characters are decent but there are too many of them. At times I was confused as to what was happening; something that never happened during the original. On the plus side it does look good with impressive backgrounds and character designs that were distinctive and in the same style as the original. Overall I'd still recommend this to fans of the original; just don't expect it to be in the same league.
These comments are based on watching the series in Japanese with English subtitles.