Licensing Legend of Galactic Heroes, a series notorious for being nigh impossible for any distribution company to bring stateside. Remember that Sentai Filmworks isn't nearly as big a company as Funimation or Viz Media, which stacked the odds against them further.
Licensing the Cult ClassicDennou Coil for the first time in North America, even including an English dub! Sure it doesn't have any extras, but to put it in perspective, fans gave up hope years ago that a 2007 production with an off-kilter premise would see a release Stateside, or that it would be anything other than a sub-only release. This definitely earned the company some cred with older fans.
The announcement that School-Live! would be getting an English dub. The show was one of their most popular 2015 licenses, their other Manga Time Kirara title Hanayamata getting a dub and the Darker and Edgier feel of the show compared to other Moe shows left fans optimistic it would get a dub. However as time went on fans became more skeptical as it wasn't in the major dub announcement at Anime Expo 2016 and it was took a very long time for Sentai to announce the home video release for it. Thankfully come February 2017 it was officially announced that the show was getting the dub people were anticipating.