I will try to judge it based in the anime only, since I didn't had read the manga yet when I watched it. But I still have to do some reservations specially regarding the character development and changes in history.
The first half episodes are quite enjoyable, I would even said that it is better than the manga begging. The rivalry between Rise and Jason, that help to the creation of the final climax, and the much darker and dreadful ambiance than what manga presents. I got truly worried about Kaneki issues.
The second half is where everything goes downhill. A lot of information bad presented or not presented at all, that always keep you in the dark. Scenes with no context, crucial scenes to the character's development excluded. The changes in the order of events don't help either, they instead made appear that Kaneki strength development is equal to none.
I think my biggest issue is how some characters and parts of the history are so radically different from manga. There is no "Yamoru" in the anime only a psycho Jason 24/7. Aogiri? These guys are to cool to you to know anything about them, instead we will just show these dialogues that don't offer no context at all. Good fights? Sorry we only have 12 episodes and we need the extra time to the no-context scenes.
Although the flaws, especially in the second half, I think that Tokyo Ghoul is quite enjoyable. The manga is far superior, but if you don't wanna read it you will be fine with the anime (as long as as you don't watch season 2).
