Why are new shows like Shield so poorly lit? Is my tv just too old and you need a 4k to appreciate it? I feel like I can't even tell who's on the screen half the time.

I get it's supposed to be moody and all, but seriously, I can't see what's happening.
New TV sets are capable of very high brightness. In fact, the very brightest modes can seem wrong and off-putting after a while [2]. Very dark scenes tend to use very little color, which can make it harder to distinguish details [3]. Many new TV sets come with HDR, or high-dynamic range. This feature keeps the detail in the brightest and darkest parts of a picture, making sure you can still see objects in shadows and in bright light [4]. 
The look of television that we’re all familiar with—brightly lit, easy to read, low contrast—was invented, more or less, by Metropolis cinematographer Karl Freund in the fall of 1951 for I Love Lucy [1]. The proliferation of large digital televisions receiving digital broadcasts changed the cost-benefit ratio for experimenting with television cinematography, but they didn’t make TV darker. The most important technologies that enabled low-light work were digital color correction and digital cameras, which made dark TV far easier to shoot [2]. To shoot that dark a sequence on film, he explained, he would need to do a series of tests—half a day, he estimated, of filming and pre-lighting to test out how each shot looked [3].