After thinking about the ending deeper, I believe many more people are going to come around and appreciate the ending, because FF7's ending is made deliberately to cause a divide and get people talking. A lot of the conflicted feelings are due to people wondering if Part 2 is going to be completely different... Which in my opinion makes no sense, because they spent a whole game showing us that the core FF7 story is still there. They've done interviews saying this. They've even been putting out a free FF7 Remake documentary on YouTube to show that they not only understand what FF7 is all about, but just how passionate they are with this new experience.
Thinking the ending change is because "lolNomura gonna Nomura" is short-sighted, and people are only saying that because other people who don't know what they're talking about keep saying it. If anyone knows FF7 the most, it's Square. They kept denying making a remake for a reason. That's why they've got the leaders from the original FF7 project plus one newer guy who became a developer BECAUSE of FF7 heading this new project. Everyone in charge has to sign off on what happens. They know.
But let's think about it for a second. The game ends, Avalanche looks out to the sunrise and rain falls. Cloud says, "We're going to stop Sephiroth." Barret says, "We're going to save the Planet." At this point in time, absolutely nothing changes, because these are the exact motivations the party had after they left Midgar in the original. Avalanche has a collective reason to pursue Sephiroth, in the original, you barely know nothing about him until Cloud has his "flashback story" in Kalm. It's just now, Sephiroth is even more of a threat than he was originally because now, he "allegedly" has seen what's in store for him and is working to circumvent that.
But Cloud doesn't know what any of that even means. Sephiroth just tells him, "Seven seconds until the world ends. I wonder what you'll do with it?" WE don't even really know what it means, that's why you have people thinking it was the Aerith stabbing, and that's us knowing "the future". So imagine Cloud trying to process it. He probably thinks it's a bunch of shyt (and it actually could be, because Sephiroth finds joy in messing with Cloud's head). All he knows is that apparently they've "changed destiny", but they're only hearing that from Aerith (and by extension Red XIII), and Aerith doesn't even seem like she really understands everything either.
As for Zack? Again, listen to what Aerith is saying. "If we succeed... If we win... We'll be changing ourselves." Square
knows that Zack being alive means a lot of characters won't be the same, Cloud most of all.
But did we actually win though? Cloud still has his Buster Sword in the ending, and the images of Zack walking seem to only be seen by Aerith who THEN says (as it rains), "I miss it... The steel sky." Before they entered the Singularity, when Tifa asks what's on the other side... Aerith says, "Freedom. Boundless terrifying freedom. Like a great never-ending sky."
Remember back in Crisis Core? Aerith was terrified of the sky. Who gave her comfort in it? Zack. When Zack died, he said "That girl, she said the sky frightened her. That looks so... Liberating." In the beginning of the game, we see an open sky. But at the end of the game, the skies are cloudy, ominous, raining. In media, whenever it rains, it's usually a sign of sadness or an omen. In other words... Even though it should be obvious since it's only Part 1... This is not the happy ending people think it is. In fact, you could even make the argument that they may even be in more danger now than they ever were previously.
The unknown journey will continue.
Vagueness Is Coming - TV Tropes