I've come across the debate among many fans of the show that an end of despair would've been a perfect and a better ending than a happy one. Regardless of that, the ending for Steins;Gate came as hugely popular and propelled the show to a high and resounding stance on the Top Anime of MyAnimeList. While it greatly satisfied the majority of the populace by having Okabe save Kurise while at the same time not altering the Alpha World Line, which also saved Mayuri. This was one of the reasons which made Steins;Gate a great thriller. Whether it was a sad ending or not, it was something that was logical and made sense.
Now this special episode titled as "Steins;Gate: Kyoukaimenjou no Missing Link - Divide By Zero" is a twist in the tale and an alternate ending to Steins;Gate. In essence, this is another episode 23 but with a following of events that is the opposite from what occurs in the actual episode. So in reality, there is only a few minutes of footage which is actually 'original' in the whole timeline of Steins;Gate and so there is a good possibility that it would be underwhelming and you'd feel like you re-watched the entire thing just for a few minutes of new, never-seen before sequences. As a matter of fact, it's only after even the credits roll out and the ED is completed that you realize that what you see now is the true preview of the upcoming "Steins;Gate 0", which is expected to be a more detailed sequel to this alternate episode 23. Everything until that feels dull and even the brief synopsis of this title on MyAnimeList would have done enough so to match your curiosity to find something new in this episode.
That being said though, the true sequel to this is still to air, so it can be said that "Steins;Gate: Kyoukaimenjou no Missing Link - Divide By Zero" is basically a hint on what is to follow and its true relevance lies on that. Right at the end in this episode, there is a scene where Makise Kurise appears on a TV-like screen and gives her greetings. I don't follow the Visual Novel so this is just my theory: From the synopsis of Steins;Gate 0, I can state that its some sort of a new program that can store memories of humans and create them with their personality and characteristics as a simulation. This might give a clue on Okabe Rintarou to try and revive Makise Kurisu, however not by time-leaping but by sending a cryptic video mail which is seen in the actual episode 23 to the Okabe of the past. This explains the pre-requisite explained by Amane that It'd have required Okabe failing the first time in saving Kurisu to work. The true answer lies in Steins;Gate 0, which I personally am hyped for to start airing.
