Overall not bad considering your height; long femurs do nake it hard to maintain a straight back as you reach depth. I have long femurs too, so here are some things that helped me:
-I would try widening your stance a bit and push your knees apart while gripping the floor with your feet. This should make it easier to get a little more depth while also potentially hitting the adductors more(good for leg thickness and hip health).
-Don't freak out too much if your knees move forward, posibly even passed your toes. For the average person, yes, try to avoid passing your toes with your knees. You're 6'8"; you're not the average person. I had "knees-over-toes" anxiety when I first started, fearing that I would fuck up my knees. Think more about the bar path; it should stay over the midfoot throughout the movement. If your knees move forward in order to maintain that, so be it.
-Give some attention to shoulder flexibility and upper-back/trap tightness. In the heavier weights your wrists would cock back; you want them straight and flexed. If you can't do this, widen your grip for the mean time and work on what was mentioned above.
-Good mornings. Do them. Gives very good attention to the posterior chain and good awareness of the glute-hamstring relationship. I personally do them with a wide stance but experiment to see what works for you. Jim Wendler wrote an article on them recently, read it.
-Get bigger legs. Squats help build bigger legs, but bigger legs also help the squat by contributing to the lever advantage of the legs. Getting your legs bigger overall will contribute to the mechanics of your squat.
Hope this helps. Getting a video up of your upper body from a side angle would help, too.