No character can appeal to everyone I guess.
I tend to like the characters better when the author doesn't take them too seriously. If they are only Hero and Cool (or Antihero and Cool, or Hero and Tragic etcetera) they become a bit hard to swallow.
I prefer when they occasionally do something stupid or have some little funny quirk. There are also some personality traits that I like more or less in characters, so it's not only about how many dimensions they have. Such as... Dune is a very interesting universe with complex characters, but there's hardly any character that I like in the books.
I like characters of both genders, and different ages, but there is a tendency towards male characters who are thinkers and keep people at distance, probably because they are more like myself. I also tend to prefer characters that are a little older, weathered and experienced to the young and pretty ones. I'm not too fond of characters that have six with anyone and all, unless it is written in a humorous way. I also tend to get annoyed when they fall in love with the wrong person, and romance is often something I tolerate rather than appreciate.