Randomly feeling like rambling about the "It's not enough" ending for a bit.
In my eyes, the "It's not enough" ending is a good example of 'bad concept, great execution'. In a story partly centered around moving on from sad occurrences, having those looming occurrences suddenly not happen after all seems like the silliest idea in the world, undercutting its own message and rendering much of what the main characters learn kinda pointless.
But there's a reason it never bothered me, at least not since I read the visual novel (I watched the anime first), and that is the absolutely stellar execution of the idea in question.
We get the choice after the 'fake' ending which is the actual ending if we decide that it's enough. Even more than that, it's right after Riki and Rin promise each other that they will go on as long as they are by each other's side. That they can and will overcome this tragedy and not lose themselves over it. Put another way, they've already gone through all the development and maturing to keep going. That's when we are given the decision.
The decision isn't that difficult for us as players, but for Riki and Rin it's a whole different matter. Going back for another try means risking not only their own lives, but everything Kyousuke and the others worked for. Riki and Rin are willing to bet all this for the chance of a 'miracle' where everyone survives. This isn't something they do because they're weak. This is a choice they make because they're strong. Because they - Riki especially - can step up as a leader. It's not easily achieved either as conveyed by the six choices in succession you have to get right lest Riki gets caught up in the explosion. A lot could have gone wrong, but getting everything right implies that Riki's choice was correct; he could take responsibility for betting the entire artificial world experience for the possibility a miracle, and bring it about by his own hands.
This is something I felt the anime sorely lacked, by the way. In the anime it feels less like Riki and Rin managed to make good on their bet and save everyone because they "do everything right", and more because they got lucky. They're a lot less calm and level-headed, and Riki succumbs to his narcolepsy. In fact you could see this as them risking everything the entire series built up to even though they don't have the strength to back that sort of bet up. It's idealistic in the same way as the VN, but it appears a lot more naive. Nowhere near the kind of leaderlike taking of responsibility that even Kyousuke can look up to in the VN.
Also, just in my personal experience, both making the "It's not enough" choice as well as guiding Riki through the process of saving everyone are some of the most poignant and gripping moments in the game. The writing is phenomenal in how it gets you attached to the situation at hand and want to see it through safely.
There's also the fact that I appreciate the notion of "A SAD ENDING? NO FUCK YOU. WHY THE HELL SHOULD WE BE SATISFIED WITH THAT? WE'RE ALL GETTING OUT OF THIS ALIVE." As in not being satisfied with an oh so meaningful outcome, but pursuing the best, the happiest one, instead. I like that a lot.