My biggest problem with Kai'sa it's not that she's beautiful - she's LoL generic beautiful.
Seriously she looks exactly the same as many other women in the game:

.
I know they might look a little different, buf if you analyze their facial features up-close, you will notice a lot of similar features. It's kinda hard to explain it in english but they all do share many similar traits, the most prominent being a small mouth with big lips.
I think Riot shold go into a more 'exotic' look. I mean, I'm gonna grab Natalie Dormer as an example (I know some people might not find her attractive, that's fine). Many consider her face 'weird' but many still consider her pretty.
I think the beautiful girls of LoL that have original faces are:
young
young
. This excluding the childs, the yordles, the robots and the ones with their faces covered.
In way, I think this is what is turning people off with Kai'Sa subconsciouly and not the fact the she isn't 'deformed'. That fact that she isn't 'deformed' it's because she learned to adapt in her new envoriment. If you're stranded in a lost island and learn how to survive, you're not suddenlu gonna turn into a panther (although this is not a very good example since the Void isn't a jungle nor an island).
Sorry for long post.[slayer-jinx-catface]
(Half of them anyway)
, who did break design moulds and stand out as unique in the roster.