I could imagine that VNs in general might be quite a bit more dependant on the state of the user, like age, gender, past experiences etc., than other genres, in order to determine whether they "click" with the player or not. Imagine someone who is in his early teens and is dreaming of some romantic companionship, or similar things, well, that kind of person would be the main audience of a game like Clannad (I think. Haven't played that one, just a guess based on reviews and videos I saw about the game). And there seems to be a really whole lot of those types of VNs floating around. In this regard, you have to take reviews of VNs with a fair bit of salt in general.
Well I haven't played a lot of them until now, but I have developed an interest in these kind of games/stories since I first played Virtue's Last Reward a couple of years ago. There was this constant praising of this game at all kinds of sites but I didn't take any of that seriously, but one day when the game was on sale and I had nothing better to do, I did actually buy and try it to see what all the fuss is about. Yes, all that praise definitely was not inappropriate. I can even say that VLR has become one of my favorite games ever... Be it the characters, their speeches (I love the original jap. voices, though I didn't understand a word, it really enhances the atmosphere as their different emotions are clearly brought to life so well), the music (!!), the ambience, simply everything fits so well together. The game also presents quite a bit of food for thought to the player outside of the context of the game itself. Well, after that game, I naturally had to play the predecessor, 999, and that was a masterpiece also of course. The third game, Zero Time Dilemma, was said to be relatively bad, well, I thought it was also excellent. Maybe not as great as the other two, but still great.
I have a feeling that there aren't that many VNs as great as the Zero Escape series, as these games already seem to be the pinnacle of mystery VNs.