The Stephen King Quantum Leap episode was really very good. Genuinely creepy (unlike the several other horror-themed episodes), and one of my favorite episodes of the show (one of my favorite shows).
He wrote an episode of The X-Files, and… it’s bad. Except for the part where Scully fries the evil doll in a microwave (spoiler alert), which seems to have been filmed to be intentionally funny. I read that Gillian Anderson thought the whole episode was supposed to be a joke and was saying all her lines sarcastically, and had to be corrected by the director. Based on the end result, I think she had the right idea.
Lots of stuff in the comic I haven’t seen. Definitely a few things to check out. I actually kind of enjoy how unbelievably uneven Stephen King TV and movie stuff is - some of it is so, so bad, while some of it is truly great.