I have a One X and a good-quality 4K TV, and after replaying games enhanced in 4K, I can say that the resolution bump provides a substantial increase in quality. Details that I never noticed at lower resolutions reveal themselves. The image is much sharper than 1080p and especially sub-1080p. I honestly cannot say I'd want to go back.
That doesn't mean I want devs to focus solely on resolution. Other aspects of visual fidelity matter as well. Next generation I hope they focus on lighting effects and shadows, draw distances (noticeable texture and object pop-in and other LoD issues are still a commonplace this generation), animation quality, and other graphical bells & whistles.
This is one of the reasons why I kind of don't understand this topic, or rather the many replies in this thread. Old games look infinitely better at higher resolutions; sometimes resolutions they don't even support.
Resolution is ALWAYS going to be one of those things that many people don't care about much in the present, why? Because you're playing games that are already at an acceptable resolution, which were tailored for the standards of today. When that happens, of course people are going to say resolution is "overrated". They take it for granted, especially in an era where remasters allows us to look at games the same way we thought they looked back when we had first played them.
It really is an important factor. Not the most important but it's up there.
Edit: Also next gen I want to see better AI mostly : )