I think it's the ratio of easiness and endurablility if these are words. There are much easier songs that get annoying very fast. I don't dislike Lady in Black but I think I would if I knew someone who learned guitar with it. Wonder Wall is more difficult but still easy to play and also remember the lyrics and sing along without being too repetitive and monotonous.
I don't think anyone obcess over their musical skills, because they're quite mediocre, but rather because they managed to pull a 10/10 album despite of being ordinary blokes with guitars.
Their second album "(what's the story) morning glory?" is a true masterpiece and should be on a top 100 of all albums of all times.
It was refreshingly unpretentious at the time. Ironically the success turned them into pretentious idiots who never managed to follow up.
I wonder how they even got into music to begin with, because it seems like a bunch of hooligans just went into a music studio and got it right on the first take.