With as few spoilers as possible, ghouls look just like humans but they eat them. As one would expect, these ghouls are quite strong and their origins are a mystery - similar to vampires in other stories. The major difference being that people are very aware of ghoulish existence.
As with many stories, this introduces an introverted, whiny weakling who is thrust in the midst of the ghoul world. Many things then start happening and it seems like the author or (if the anime strays from the manga) producer loses track of things and doesn't tie up loose ends.
The transition from the second into the third season is abrupt and most characters are just referenced to later on. Many things remain unexplained as major characters were introduced throughout the second and quite big reveals are made at the end. The reasons for the main characters action however, stay shrouded in a veil of pseudo-psychological justifications.
The unfinished story aside, the animations are crisp and well-done, and the story has a good pace, but I couldn't bring myself to watch past the first episodes of season 3. The disconnect was and lingering questions were very annoying.
A very good anime for people who like theory-crafting, but for those without that time on their hands who want a nice bow on a story, skip this.
