The most genuinely underrated show to me, as in not even like Halt and Catch Fire where it's underrated by general population but has some boosters, is probably ABC's Once Upon A Time. The reason being on paper a network drama with Disney characters like Snow White is probably the most unlikely great show you can have, it should've just been some trite cash grab 99 out of 100 times. The only thing that would be more unlikely is if one of the network procedurals was actually a great show. I just think some people could never get past their initial bias, even some of the people who watched it I think weren't doing it the right way by engaging with it only as a stupid guilty pleasure. I think the writers were actually taking their characters and large scale storyline as seriously as Lost in reality, it's just its concept is not as cool on paper or male friendly as the island. I have a fantasy that one day people will get it and recognize it more as one of the best sci fi/fantasy genre shows. I have that/BSG/Lost/Walking Dead as my favorites.
An underrated comedy from this era for me is the Mindy Project, however I understand comedy is subjective and I'm not going to blame people if they laughed more at other stuff. The jokes worked for me. I liked that Mindy was doing a twist on the romcom and fantasy vs reality. The Danny stuff played tribute to it but also subverted it eventually. Personally I think this show is better than stuff like 30 Rock and Parks and Rec that got a lot more attention in its time.
Other mentions
Halt and Catch Fire - brought it up before, great 2010s drama, although I'm not the only fan
Broad City - I really like the physical comedy and chemistry of its two leads. The first season is probably one of the funniest I've ever seen. This is one I'm really surprised hasn't caught on streaming more, it's basically a walking meme. I guess you have to be on Netflix.
UnREAL - not a perfect show, but probably one of the most unknown above average shows. You know that movie Hostel where the characters get kidnapped so rich people can pay to watch them get murdered, but the point is that you the viewer, are kind of doing the same thing as them getting off on watching a gorefest. That's what I think this show is kind of like for reality tv, it's kind of skewering it, but at the same time, you're into it for the same reason as the viewers and still want to know who wins the season.
Populist hits that are underrated quality wise:
The Walking Dead - I think this was extremely good, or at the very least the first half of its run. I thought it great cinematically, human storylines about fighting to stay alive mentally (reminded me of Battlestar in a way, with zombies=cylons + Bear McCreary).
American Horror Story - I really think this show is impressive and unique artistically, I like the editing style. The characters usually are on emotional journeys. It's not just "Let's do crazy stuff and shock people" with nothing underneath imo, it has a purpose.