Currently watching Vikings, I've seen it before but I'm re-watching with my folks. I think the earlier series are the better ones, but the later ones have their moments.
I loved Walking Dead, so much more than I was expecting. I'm rather fond of the post-apocalypse setting so it already appealed, but I liked the fact that it was often used more as a backdrop than the sole focus. Again, the later series got a bit samey.
Breaking Bad was also great. The character arcs in that show are exceptional. Same with Better Call Saul.
All of those I avoided at first. They all seemed mainstream to a silly degree but sometimes things get famous for good reason.
Some others I've enjoyed and feel are a little underrated are, Umbrella Academy, Dirk Gently, Happy (wonderful dark humour in that one), Ash vs Evil dead (really stayed true to the films and I loved it), The Sandman, American Gods (gutted they refuse to finish that one), Altered Carbon.
I watch a lot of stuff thanks to having to take breaks all the damn time. And on the days when I just can't get going I try and settle into something. I usually have something on my second screen while I'm on a game or writing, it's always a good sign when it grabs my attention enough to focus on it
The one that goes the other way is Game of Thrones. I like fantasy but I really didn't see the appeal of that. I was given a box set and watched a few but it just got on my nerves. I've got no idea why it got so much hype. It just seemed intentionally convoluted and up itself.