Well, I dislike it a lot so I'll bring up why and then get yelled down for being a whiner or whatever.
In any case, let's make something clear. The old lore was never very good. Unfortunately, the new lore also isn't very good. There's more of it, but the quality of that lore is really lackluster, in my eyes, and the changes made are often very strange and not exactly necessary except as a means of forcing the elements into the lore of the stuff I really don't like. Taking the few parts of the old lore that actually were good or at least interesting and either pointlessly altering them or replacing them with strange things that don't interest me at all.
The big one is of course, the Aspects themselves and how they warp everything around them. From the old lore, Leona was still Leona, Diana was still Diana, they simply got a power boost from their gods. But every mistake they made was still them. Compare that to what has happened in the new lore, and Leona was acting as Leona right up until she gets possessed and then suddenly her entire personality changes to match with what she was before the lore change. Which is unnecessary and kind of weird.
Really, Leona's entire story is muddled. At first, she acts like the Leona the original fans of the character liked. She stepped up against the codes of the rather barbaric Rakkor, and got herself almost killed for her conscience. Good, that's exactly what her fans wanted to see. Then, she goes to live with the Solari, and suddenly her personality changes. Now, I am sure that the argument for anyone disliking her personality change will say "Oh she was always aggressive, she has a sword" or "Now she has more depth" but I really don't think that's the case. For the first part, there's a difference between being aggressive and what Leona actually was in her new lore.
In her new lore she is literally fantasizing about killing Diana the first time they meet because Diana was saying things she didn't like. Not doing anything wrong, this is before she kills the Elders. She's just talking and Leona is reveling in her role as an executioner. Which, none of her old fans really saw her as. But then we know how that plays out, Leona runs up the mountain, meets the alien thing, gets possessed and suddenly she's fine with Diana again.
Why that's strange, because that is literally Leona's personality pre-retcon, and at the beginning of her own lore. Her sudden shift of personality doesn't add anything, in fact since it wasn't explained why she changed or how it really just comes out of nowhere as sloppy writing. Where the characters personality is warped to get the effect that the writers want without paying attention to what a character was before that point.
Even stranger was how Riot itself seemed to kind of ignore the retcon. At the end of both their stories, Leona is fine with Diana and wants to share their knowledge and Diana is trying to find peace with the Solari (which is not at all what her in game dialogue is like, but whatever, I assume that will be changed when they get around to updating dialogue for non-reworked champions sometime in the next 3-4 years or so). But then a month or so later, Riot made a big poll event about who would win in their grand rivalry, Diana vs Leona. But, the rivalry was just written out of their lores, Riot members even said in the thread that yeah this rivalry is no longer canon, and yet their rivalry was still such a huge part of what the community sees in them that they're still setting up events around it.
Which goes again to promises, set up, and execution. For the few folk who liked and even cared for the old Leona and Diana stories, the writers and designers were dropping hints like crazy that there was more to the Leona and Diana relationship than we knew. That their meeting would be a heartbreaking thing. And, it was set up in a way that I personally (and this is only personally) found interesting. Because in the old lore, Leona was definitely the "good" person. But she was also unequivocally on the wrong side, which I love when that sort of thing happens. The Solari were the ones who were attempting to stamp out the old Lunari knowledge, she didn't know that, and it created this tension of seeing these two paragons having a theological battle that would be made across the mountain.
The other thing I have against it, is really the entire star empire possessing alien things. Which, reading it I thought was one of the strangest most unnecessary additions to something I have ever read. But this has to do with what I find interesting. I like history. I like normal people dealing with the political and social fallout of their actions. And, I'll admit, I had built up what the Targon lore would develop to in my head, but it seemed so obvious to me. The Solari were leaderless, and they were the religious and vaguely political bodies that ran the entire mountain. The Lunari were on the rise looking for allies to change the political balance of the mountain. And the Rakkor were still there, the wild card warriors, would they choose the Sun or the Moon? And who else would be dragged into this political struggle. That stuff fascinates me.
Then what we got is that very interesting story shoved aside to focus on aliens, with a star empire we never heard of before. The champion that I really liked for being a normal soldier who could fight these monsters and gods, became a really awesome soldier guy. Then got possessed by another alien, and somehow that alien was just as bland and characterless as the character was before the retcon. I mean come on, Riot, I will not say that old Pantheon was a great character. He wasn't, there was stuff there to develop from. But the new Pantheon? He's just as bland, only instead of a Spartan he's a Goa'uld. He still doesn't have a character. In fact he barely registers in his lore, he shows up the last couple paragraphs to kill a few raiders and we get a vague warning about future terrors.
And that's not even getting into the somewhat sloppy little details that Leona's and Pantheon's lores don't even line up properly in a timeline.
Now, I will say. Taric's lore? Actually pretty good. But as a whole the story that those who enjoyed the old lore were waiting to see got rather violently pushed aside in place of dealing with a space empire and star dragon.
If you like the new lore, more power to you. I hate it. It took an event I was looking forward to, a political and social drama of soldiers and ideals. And turned it into a people getting possessed by aliens. The drama I wanted to see barely registers when compared to a world ending dragon and void threat. But, again, I don't care about Sol, or the aliens. The new lore didn't get me to like or become interested in the new story they've delivered. Instead I'm just vaguely rooting for Sol to burn the space Targs all up and leave Runeterra alone.
But even then, what really confuses me. If Riot really wanted a space empire, with a light/dark dichotomy, where the light side probably isn't as good as you'd think, forcing their conflict to come to Runeterra. Well, that's literally what Morgana's and Kyle's lore were set up as. Why didn't they just use them?
Though I will say, the vitriol about the lore change has definitely gone down. When it first happened, there were a lot of people who complained about it. Now, most of them seem to have stopped posting, and a few have stopped playing the game entirely. But, that's to be expected I suppose. It has after all, been months.