I have tried several animes, mangas and visual novels with art styles that I initially found ugly. But as long as the story is captivating, I get used to the art style or maybe start to like it, and it doesn't bother me anymore.
I don't find the clannad art style ugly anyway. When I was young I used to collect pictures of anime girls and most of them were probably from key visual novels, I even watched all key animes at the time for the art even thought I didn't greatly enjoy the story and found the stories weird and confusing.
What really bothers me is bad art. For example, I really like the art style of steins gate (especially the eyes), but the CGs are often bad, as if they gave the job to someone who's still learning and makes amateur mistakes or had no time and drew something super quickly. Sometimes even I could have drawn it better.
The art style changing slightly also bothers me, because I have already gotten used to one, and now the two art styles are clashing in my head. For example, in steins gate mayuri looks kind of different in steins gate 0 she looks like a nice mature girl while in the other version she looks more like the ditzy girl she's and there's a charming gap between her appearance and character.
