Kudos usually mean "I liked this" from me, but, under certain circumstances, they can mean "I adored this." Usually when I like something that much I leave a comment, but the older a fic is, the less likely I am to leave an actual comment. It doesn't matter how much I enjoyed an epic in fandom X that was written in 2002, odds are pretty low I'll leave a comment on it. But I will leave a Kudos.