A large part of this fan base is super adamant about the manga being infinitely better than the anime. Personally I feel Root A kinda did that statement a bit of justice.
Season one, cut off at a decent point leaving Root A, with a good direction to go to be a phenomenal conclusion (Barring that the ":re" manga sequel doesn't get an anime adaptation), but it kinda did it's own thing. Which in all rights is fine to do, but it left more questions unanswered than answered, and kinda left a sour taste in my mouth.
I'm a part of the population that likes it more when an anime stays strict to the manga instead of doing it's own thing. So overall I'd give Root A, a 7/10 just because the art was pretty to look at, and the music was decent.
In short, if you're just looking for Tokyo Ghoul content, Root A is a good way to go. But if you're like me and like series staying stricter to the manga, this is a series where you should probably just read the manga.
Side note: If you don't want to read the entirety of the manga after watching season one, chapter 49 isn't a bad place to start. That chapter is right around where stuff starts to get ominous at Anteiku before Kaneki gets kidnapped by Aogiri.
