To the OP and others: Be wary of Blu-ray when renting or buying used discs from anywhere. There are known issues with discs being flexed while mailing or kids trying to cram discs into slot loaded players. If the disc is flexed, the media becomes damaged even though the disc from a scratch perspective may look perfect.
You may enjoy the disc just fine until you reach a point where the media has been flexed then it will lock up, usually near the middle of the disc, and then the only option is to skip ahead to the next chapter and attempt to scan backwards until the disc locks up again. Renting an older series on Blu-ray like Dexter or True Blood that has been rented and shipped hundreds of times is an exercise in frustration and aggravation.
On severely flexed Blu-rays, you can hold them up to a bright light source and see the wavy flex marks in the media itself. This seems to be less of a problem with older DVDs, and I think because the media is more dense and closer to the surface of Blu-rays this has become more of an issue with them. I'm sure the 4ks will be even worse regarding flexing issues.
And the only time I ever have any problems playing a Blu-ray is if it is a rental, sent by mail in a flimsy paper mailer. If I rent the same title from my BB store or buy it after having some problem, then they ALWAYS work.
And the HD Blu-ray mastering is in all cases vastly superior to DVD mastering if done right. I would imagine all they are doing on the new 4ks, is increasing the sample rates on the original Blu-ray masters to get the extra definition, and not much else. Now, with 3D, they may actually finally have a valid reason to use 4k more often, besides just for projector use or on MUCH larger displays. Which is why I couldn't care less about 3D in 1080P on a 60" screen.