I have been reading Stephen King since I was about thirteen and I think that he is rather easy to understand. (Maybe I am weird like that.) But the greatest help when it comes to understanding his work is, in my experience, is knowing that Stephen King writes about the things he is afraid of. So whatever freaks him out, he writes about. In regards to his work that is more supernatural, he tends to over-write those parts and goes into great detail when describing those things. To understand those parts of his writing, simply read those sections slower and it should make some sort of sense. Always remember that though Stephen King is one of the most realistic writers, meaning he writes in the real world sense, he also writes in the out of world sense. Everything he writes needs to be taken with very open minds.

Hardly any of his books interest me beyond his Dark Tower series, and I still don't think he's a very good writer. He writes by the "seat of your pants" method, and it shows, particularly so in the Dark Tower. You have jarring inconsistencies of quality and pacing, sections that drag on too long, and a plot propelled by characters saying something like, "Don't ask me how I know this, but..." Not to mention how he has an annoying fat fetish. Whenever a fat chick shows up, he'll wax poetic about her mountainous rear end, and I'll sit there thinking, "For God's sake, Steve! Nobody wants to read that!" For much of his career, he also wrote to supplement his family's income, which is why so many of his books are basically the same story with all the proper nouns swapped out. Too often he depicts a writer with personal problems assailed by a formless, unknowable evil in small town New England, but that's not nearly as relevant to me, since no books with that premise appeal to me.

Basically, he's more frustrating than anything else. He's got a few great ideas, but I know he could do so much better. However, I really don't know what you mean by "complicated to read," but then again, I haven't had that problem with a book since the Paradiso section of Dante's Divine Comedy.

King is an acquired taste, I'll say that much. You certainly have to have patience with him to get into the good parts because he likes to explain everything very, very thoroughly. However, once you get past the dull explanations, you'll really enjoy his work. I'd say start with something like 'The Shining' or even 'Carrie' . I know, I know, they're the "mainstream" King books, but they're easy to comprehend, and actually, 'Carrie' is pretty fast paced for Stephen King work.

Black House is not one of his better ones, mainly because he tries so hard to tie it to his Dark Tower series. The Talisman, the first book in that series or whatever it's planned to be, is much better (IMO) because he lets it be its own story. Black House gets taken over by his need to tie everything he writes into the Dark Tower storyline. It feels like a bunch of horror scenarios he created a while back but never got to use, stuffed in alongside some characters he created a while back but never got to use, knotted around the DT series in a desperate attempt to hold it all together.
I did like some parts of Black House, but it will never be one of my favorites. Not to mention I wonder if Peter Straub had a hand in any part of Black House, aside maybe from the opening image (I think it was a bird flying over the town?) and the egg- those sounded like him but were about the only parts that did. (Note: I read Black House about 4 years ago and do not remember it completely)

I'd recommend trying some of his short story collections, like Just After Sunset and Everything's Eventual. These are good because there are usually author's notes about where he got the idea for each story, and they're short enough that you don't get overwhelmed by a huge cast of characters and big backstories the way you do in most of his novels.
Quite a few of his shorter books are easier to get in to than the super long ones. I'd recommend The Girl Who Loved Tom Gordon, The Bachman Books (especially The Long Walk), Cujo, and Carrie.

Aside from that, keep in mind that most of his recent books are written around the idea that everything he writes has some connection to his Dark Tower series. Personally, I really liked spotting all the little similarities you could trace from one novel to another, at least until I read the last few books in the DT series and he explained it. After reading that, it feels like a lot of the tie-ins are kind of desperate and/or unnecessary, but maybe that's just me.

I could never get into most Stephen King books (and believe me I tried) but two of the books I enjoyed reading were Under the Dome and Pet Semetary

I wouldn't consider his books complicated. I've never been able to get into them though. He doesn't seem to have anything interesting to say, nor an interesting way of saying it.

I remember reading his novel "From a Buick 8" about two police officers in west Pennsylvania investigating an old Buick that was supposedly haunted.

They're not hard to get into because they're complicated, but because most of his books are very linear and slow. He goes from point A to point Z without skipping any letters along the way. He slowly builds the climax throughout and then hits you with it. Unlike other authors that try to keep your attention the whole way with cheap gimicks, King simply tells a story.

Good luck. All I can say....

To be honest, I've never really REALLY been into Stephen King the horror author. While they're undoubtedly good stories, horror just isn't my thing.

However, I am completely and absolutely in love with his epic The Dark Tower fantasy series.

I'm fine with King's horror short stories, but I find it hard to get emotionally invested in a lengthy horror novel. No criticism on writing styles. Just that horror isn't a genre I particularly enjoy.

I enjoyed The Shining and his short stories. I was not interested in any of his other books, they start off great but then I lose interest towards the middle and never end up finishing them.

I guess it would depend on your reading level and past experiences. If you're used to reading light fluff books, Stephen King could be understandably hard to get into because he oftentimes drivels on the details and can spend quite a long time worldbuilding and character-developing (as opposed to getting on with the story, which can be boring to some readers who just want fast-paced writing). A lot of his books spend hundreds of pages going through Bob and Sue's sometimes mundane lifestyles before the real meat and potatoes of the story is explored. And some of his books, in my opinion, are just simply bad and ARE boring to read (*cough Cujo cough*). I've never read Black House before, but I've read several of his others. That's just the way the man writes. I personally like it. xD His words on the human condition I find very interesting to read.