This pertains to Kanon(2006), I never watched the 2002 version since it kind of creeped me out. The beginning parts talk about Air and Clannad, and some exposition, you can skip the the third paragraph for the actual topic.
When I was younger, the Key anime series were a big thing. It might still be, with Rewrite, Angel Beats and Little Busters; I don’t really know and it’s not really important for the topic at hand. But Clannad, Kanon and Air were the big three, each having their own successful anime(not sure on 2002 version).
For the most part, the novel will be better than the anime but it requires a much longer time to finish. Is it worth it? That’s dependent on the person. For example, Air’s anime adaption to the main route was well done, but Kano barely has any air time(Minagi was done much better, but of course not fully due to route issues with the main route). On the other hand, I felt the final scenes in the anime was much more emotional than in the vn, even with a more developed understanding of everything(though Minagi emotional moment was done better in the vn). It’s mainly a trade of a complete experience for a much more effective time frame.
It’s kind of the same case with Clannad(this whole paragraph is about Clannad, you can skip it), the anime adaption was solid and it saves so much time compared to reading the vn. Yet, while it’s solid, it also missed a shit ton of details(some important, some not). Something not so important would be Kappei’s route, but it was a great route. Toshio is a much lesser example than Kappei, but I was also rather sad in his small route. Kotomi’s route was done better in the anime, but misses a lot of scenes that are endearing. Naoyuki was done better in the novel, and I also believe Tomoyo was done better as well. Yukine’s route, however, was much better in the anime. The rest are kind of dependent on the person, but I believe Naoyuki(MC’s dad), Tomoyo and Misae was done better in the novel. There’s other points but you get it already. Outside of these minor details, the whole story is explained better in the novel. The anime just shoves it off and basically call it magic, which kind of destroys part of Tomoya’s journey and emotional growth.
Now we’re finally hitting what I wanted to talk about, the rest was exposition like I said before. Let’s just get around to what the novel did better so it can get out of the way. I feel Nayuki and Shiori’s routes were done better in the novel than the novel. And that’s it. Makoto is a huge little shit in the novel that she’s basically a saint in the anime. Mainly because her antics keeps on going for so long. Mai’s route doesn’t really change at all, it’s basically the same. Ayu’s route isn’t as emotional in the novel as it is in the anime, at least for me. In short, I can understand why the anime can’t be as good as the novel overall. But when the anime does almost everything better, there’s almost not point in reading the novel. Outside of one point.
That point makes this novel more of a utsuge(depressing) than a nakige(crying). I’m probably wrong with it but that’s how I interpreted it. In the novel, you can cause one miracle. For example, save your aunt, save your girlfriend, etc. Now, the miracle comes from a certain girl(now called X), and she’s forever gone once it’s used, so you effectively killed her for your own reasons. The aunt is kind of situational since it only happens on Nayuki’s route, so let’s say that happens only there. So you saved your aunt, which is great, but you actually killed ‘X’, let Shiori die and Makoto is technically dead as well. You save Shiori, but now the others are dead. You’ll always have to make a sacrifice. In the anime, basically everything is A OK(my memory is fuzzy on Shiori but I think she got better too).
In short, there’s good and bad between the two, and there’s different nuances that change parts of how I see the story. I feel like the anime ended better, not because it’s an overall happier ending(which I believe so), but it was just an ending that had you care more Ayu than in the novel.