Some times when I look at things in 720p, mainly videos, the blurry text can bother me and prompt me to change the settings to a higher resolution. But that's different from gaming, since a lower resolution of a video wouldn't produce a native image, which can cause it to be more blurry.
When it comes to games 720p is usually just fine. And anything beyond 1080p is unnecessary to me at this point.
I think 1080p is always gonna look good. We're just at point where going above 1080p is easy with affordable specs. I mean its matter what looks sharp to the human eye and 1080p is just that.
Although the nice thing about games running natively above 1080p is the improved visuals on that same 1080p screen. I'm referring to super sampling and it creates an overall better image even if you don't want to upgrade your display resolution. 16x anisotropic filtering is also great for improving the clarity of textures.
Essentially 1080p is that sweet spot resolution that will always be crisp to the human eye and we can still see improvements of higher native resolution and post processing effects. 4K will become the new standard eventually, but its not as crucial at the jump from 480p or even 720p.