I love Salem. If you're a fan of horror and you aren't watching it, you're missing out. It's kinky, it's dark, it's gruesome, it boasts a fantastic cast, and the soundtrack is equally impressive. I really don't want to say much about the plot. It's about witches, of course, but it's really fresh and exciting. I think this is definitely one of those cases where the less you know going in, the more you're going to enjoy yourself. The show's creators may have felt the same way; the previews were intriguing but didn't really give a lot away, and I've been surprised and delighted by the program from the very beginning.
Bonus points: In addition to stealing the show as Cotton Mather, Seth Gabel has a killer beard. I've never seen this dude in anything before, and while the show is brimming with quality performances, he's been a bit of a revelation. He's good, really, really good.
Under the Dome is a different story. I really enjoyed the way the first season started. This is when the series was being a bit more faithful to the book, but King intrigued me with all his talk about taking the show in a different direction and presenting a different conclusion. Early in the second season, I think it's become obvious that this approach was a dreadful mistake. Hey, if you like it, you're free to watch it, but I think a very promising series has devolved into garbage. I don't think I'm going to keep watching it; Season 2 has been downright painful. Whereas the book (a top-notch affair with a somewhat lackluster ending) focused on the people and the human conflict playing out under the dome to great effect, the show has become more of a mediocre CGI and bizarre plot twist showcase.
It's depressing, particularly when you look at the cast and think about what could have been. The talent is still working hard to make it work, but plot holes, massive gaps in logic, and poor effects have ruined a program I was really enjoying early on.
Anyway, if you're not watching Salem, join the party--it's a wicked good time. And if you're still sailing with Under the Dome, well, may God have mercy on your soul.