Wow, wow, wow! Usually sequels aren't all that great, but I LOVED catching up with Dan Torrance.
Doctor Sleep definitely has some scary moments, but it's more of a creepy thriller than all-out horror novel. I'm sure this will disappoint some people, but I loved it. The plot draws you in and makes it really hard to put down. Dan and Abra are great, and the supporting characters are excellent as well. There are a lot of references to other King novels, which I loved, but someone who hasn't read his other novels won't feel like they're missing something essential (I also loved that Charlie Manx and Christmasland made a cameo, even though I wasn't a huge fan of NOS4A2).
That being said, you DO need to read The Shining for this book to make sense. If you've only ever seen the movie, you have to read the book before getting into Doctor Sleep, or you will be really confused.