[EDITOR'S NOTE: Warner Bros. Home Entertainment provided me with a free copy of the Blu-ray I reviewed in this blog post. The opinions I share are my own.]
The Warner Bros. Home Entertainment September 17, 2019 separate DVD and Blu-ray releases of "Supergirl" S4 brings us 3/4 of the way toward completing these releases of the 2018-19 seasons of the CW Arrowverse series ahead of their (mostly) October 2019 season premieres. "Supergirl" S4 follows the (reviewed) sets of "The Flash" S5 and (reviewed) "Arrow" S7. The September 24, 2019 releases of "Legends of Tomorrow" S4 completes this run.
The reasons for springing for the BD sets extend (except as to "Legends") beyond those versions including the epic three-part "Elseworlds" episode that introduces Batwoman to the Arrowverse ahead of her 2019-20 series. Past lack of buyer's remorse validates that spending a few extra bucks to get the deeper and richer color and sound of BD is well worth it; this is not to mention BD being less prone to the ravages of time and repeated viewings than DVD.
"Supergirl" always has been more closely aligned in lore and tone with "Flash." On-screen, this relates to Barry Allen (Grant Gustin) of the latter introducing Superman cousin/reporter/covert government operative Kara Danvers (Melissa Benoist) to the Arrowverse. Further, both series skew younger in cast and target demographic than "Arrow." Off-screen, Gustin and Benoist (who have sung separately and together in their current series) are former Gleeks,
Further, "Flash" and "Supergirl" both revolve around boys and girls with something extra on both sides of the law. These problems and solutions mostly are aliens on "Supergirl," and mostly Spider-man style meta-humans who accidentally acquire special abilities on "Flash."
Conversely, most of Team Arrow and their foes are more like Batman in that they use advanced tech. in their efforts to put their well-honed skills to good (or bad) use.
The underlying debate on whether aliens, most of whom can easily send us muggles crying home to our mommies, in "Supergirl" S4 parallels the underlying theme in "Flash" S5 regarding how to handle a "cure" that makes a meta like other boys, The options there are to completely suppress the cure, make it mandatory, or give metas the freedom of choice.
As a side note, both "Supergirl" and "Flash" also have an annoyingly cartoonish "Scrappy-Doo" style/outcast character who fails in his mission to provide comic relief, "Flash" compounds the error as to acrebic scientist Harrsion Wells by making the current incarnation of him stereotypically French,
"Supergirl" has a kinder and gentler version of Brainiac, whose voice and misunderstanding of life on that alternate earth are inconsistent with his supposed intelligence, The writers mercifully limit a quirk as to referring to classic films to a few episodes To expand on a reference to the game of three in the "Flash" post, neither Wells nor "Brainy" would fare well regarding that diversion.
A real-world analogy in these series by openly homosexual executive-producer Greg Berlanti is gay rights. One aspect of this real-world non-issue is the "threat" that LGBTQ folks pose to "normal" people. An element of this in the entire Arrowverse and our reality is that most of the "villains" can "pass" for "normal."
Everything regarding this in "Supergirl" S4 ties to the Children of Liberty, lead by Agent Liberty (a.k.a. former US history professor Ben Lockwood) which loosely can be described of as a human-rights organization. The analogy as to this group that aggressively supports a "send her back" policy is to the related issues of immigration and refugees. This encompasses "them" coming to "our" country where they take jobs from "real" Americans and cause extensive physical destruction. We further see how these negative experiences can radicalize folks who previously largely avoid the maddening crowd.
The Children's campaign to repeal the federal Alien Amnesty Act does mirror a theme in "Arrow" S7. The legislative effort there is to outlaw vigilante activities of Team Arrow that supplement formal law-enforcement work.
An early "Supergirl" S4 episode begins to eliminate confusion as to that season seemingly not addressing the S3 cliffhanger. The final scene in the season finale has our heroine landing in what seems to be eastern Europe. The additional S4 exposition is that this individual can be considered a version of a bizarro Supergirl.
More exposition regarding all this comes roughly 3/4 into S4 with the heavily anticipated first appearance of Jon Cryer as "Super" nemesis Lex Luthor, Fanboys will remember Cryer as gonzo Lex Luthor nephew Lenny in "Superman IV: The Quest for Peace."
Aside from this introduction of a major DCU character into the Arrowverse series, the coolest thing about having Lex Luthor join the party is seeing late in the game how he orchestrates so much from the sidelines throughout the season. His "great escape" is another highlight.
All of this leads to season finale that includes an extended thrill-a-minute climax. The cliffhanger hits a high note by (ala "Arrow") bringing back a central "Elseworlds" element and keeping fanboys on the edge of their futons until the October 6, 2019 S5 season premiere.
The bigger picture is that S4 arguably is the best "Supergirl" season. It has streamlined characters, made Kara far less awkward and geeky "Ugly Betty" like, and has stronger story arcs.
The biggest picture is that the latest batch of Arrowverse seasons supports what fanboys have known for decades; comic books are about much more than men (and women) flying around in Spandex.
The plethora of S4 extras include a presentation of highlights from 2018 Comic-Con panels of Arrowverse series, a (Blu-ray exclusive) feature on "Elseworlds," a look at DCU super villains, deleted scenes, and a gag reel. The deleted scenes run from the sublime to the ridiculous, and the gag reel shows which cast member is most prone to cursing.