I will admit up front that I am a Marvel fanboy. I enjoy D.C. comics and movies as well, but I am a particularly big fan of Marvel. So this is not an unbiased argument I am about to make. Also, if for some reason you are reading this without having watched the show, there may be spoilers.
I think Marvel's Agents of S.H.I.E.L.D gets more grief than it deserves. I think it's a pretty good show that is made great by its connection to a larger universe. People complain about how long it took the show to really start telling its story, and start developing its characters. I would argue that a good story takes some time to set the scene and introduce the players. Besides, if you go to Netflix and binge watch the first season, you will see that they started telling the big story very early on. It was just done so subtly that those of us who were watching the original broadcasts mostly did not notice. The alien writing which was such a big part of the plot up to the midway point of the second season was introduced in episode 4.
Another complaint is that the show took too long for big reveals and stretched the story out too much. I will admit that there were times when it felt the story was being stretched for no good reason. But other times it was necessary to make for a better story. Ward's reveal as a Hydra agent would not have been nearly as impactful if it had taken place in the first few episodes. We needed that time to get to know his character and watch him bond with the rest of the team for that moment to have the effect that it needed to have. That is why that is a "Wow, I can't believe that just happened" moment rather than a "Meh, saw that coming" moment.
The one thing I read most often about Marvel's Agents of S.H.I.E.L.D. is that if it were not for its connection to the MCU, it would not be as popular. It probably would not, but this is still a ridiculous statement. Yes, part of the appeal of this show is its connection to the larger movie universe. That connection is a part of the reason the show exists. It is there to tell some of the stories they do not have time to tell in the movies. Saying the show would not be as good without the connection is like saying Sofia Vergara would not be as hot if she had some sort of weird growth right in the middle of her forehead. But she doesn't, so there's not really an argument there. Some try to make the point that they don't want to have to see the movies to enjoy the show. Guess what, you don't. While you will definitely get more out of the show if you watch the movies, you can still follow the story pretty easily without doing so. Personally, I don't understand why someone who doesn't want to watch the MCU movies would want to watch a lower budget version of them on television. It would be like someone who doesn't like Superman trying to watch a show all about Jimmy Olsen. That show would only be interesting to someone who is invested in the Superman universe. The same holds true for S.H.I.E.L.D.
Finally, the last complaint I kept seeing was that this was a superhero show that did not show any superheroes. My initial response to this was that they were mistaken about the purpose of the show. The Whedons were pretty upfront that they were not making a superhero show. They were making a show about regular people trying to cope in a world where superheroes exist. While there were people around the team with powers, the team themselves were just regular people. That was part of the point. Of course Skye now has powers, so that whole premise has changed. To be honest I'm a little sad that a member of the team has turned out to have powers. But that is overshadowed by my excitement that it appears that the show runners have decided to use S.H.I.E.L.D. to introduce characters and concepts that will be used in the movies down the line. That is super cool. I think a lot of the initial disappointment was due to people thinking that Robert Downey Jr. or Chris Evans would pop up. That was unrealistic. This show was only ever meant to deepen the background of the MCU a little. In my opinion it has succeeded at that quite well. And Ming Na Wen is hot, just saying.