The thing about Key is they have unexplainable disease and they have magic to save the characters.
To be perfectly honest, I hated it. When I first watched AIR (my first Key series in line) I was like whaaat. What the hell is with this girl cursed or reincarnation or whatever it is. What the hell is this guy turning into crow and sh*t and such. And instead of getting tears like how people should, I was there befuddled “Where should I cry? What part is the sad one?” Though ultimately Misuzu “goal” scene made me cry.
In CLANNAD, the supernatural element is quite small in portion, so that’s why I like CLANNAD. The story is full of tragedy but it doesn’t feel like out of this world. The same thing could happen without your knowledge to someone close to you, maybe your neighbor, or your classmate, or even you (I hope not though). The VN was great but the TV anime adaptation, in the other hand, forced the magic to happen which lead to a few people disappointment. There are tons of theories but I found them really stretching it out. My opinion to enjoy the show is to forget how the magic works. It just happened. You don’t have to understand how TV works to watch it. You don’t know if it’s filled with tube, LED or tiny gremlins. They just work like that. Period.
Key magic is, I think, way too convenient. In CLANNAD TV Anime and Little Busters! the magic worked reviving the dead and I do feel like it’s not really a “strength”. Instead of doing human transmutation to revive your late mother, it’s wiser to do something else to move on. Yep, it’s sad to be left by the ones you love, but you can’t just cry all day thinking about how great if they were still alive. Such wishful thinking would lead to depression and escapism. Instead, think of “How should I go on now without them?” Find a new meaning of life, find new friends etc. You shouldn’t forget of those precious ones who left you, but you really can’t accomplish anything by thinking of them all year around.