The Sacrifices series, starting with Saving Connor, is complete and something like three million words. Harry's darkness is an ongoing debate, with plenty of people insisting he's a dark lord. He uses dark magic and has plenty of dark allies (ex., the Malfoys), but does use some light magic on occasion. Well written, AU (Lily and James survived and raised Harry and his twin brother, Connor), with a ton of world building and some very well written fights between Harry and Voldemort. Fair warning, the romantic pairing is Draco/Harry, and Harry is excessively strong.

Also I haven't actually finished it yet (I'm a quarter of the way through year five), so I can't say how later events change things.