Brilliant TV series. Much better than I was expecting though it takes a few episodes for it to sink its hooks in. The series begins with the ending and from the second episode the story is told in the form of a flashback. It takes a few episodes before you get a grasp on exactly what it is that's happening as it slowly sets the scene and puts the players in place.
There's a lot of aspects that make this series go great. Its got well developed and believable characters who all have complex personalities and realistic motivations for their behaviour and actions coupled with a nice mix of horror and fantasy but grounded in a sense of reality so it's never too hard to suspend your disbelief. Most of the time the horror/fantasy aspect is kept to the background so the emphasis is on the relationships between the characters and the main story of a band of mercenaries who rise to great power under the leadership of their charismatic and extremely ambitious captain Griffith. It's not perfect as the animation is clearly low budget and the ending doesn't really come to a conclusion which means ultimately if you want to find out what happens next you'll need to buy the manga (which are still ongoing). These are minor flaws though and the story and characters are so good that they more than make up for any shortcomings.
If you don't mind lots of bloodshed, violence, and some dark and grotesque images, then there's no reason you won't find this highly entertaining and engaging viewing.
