I have read all of the Frank Hebert novels several times and adore them. Even God Emperor of Dune. I have never read any of the Brian novels because I hear they are such trash. But now 40 years after first reading Dune I am starting to question that decision. Should I?

Do it, its the only way you'll know for sure if you like it. Personally, I explicitly like Dune and that is it. But hey theres a bunch of whacky shit in there at the end on Rakis.

If you've read all the OG Dune content, I say go for it. They aren't at the same level, but they're... Fine. Get it from the library or wherever and try it. Go in with low expectations and possibly get pleasantly surprised, or never pick them up again.

No. There are so many productive ways you could spend your time instead.

I would give them a miss, you can probably make up better extrapolations in your head and there is so much else to read.

What you have heard is nonsense. Read them all, soak it up.

They're pretty okay, definitely expands on the universe, so if you just can't get enough Dune, I'd say give 'em a go!

They arw one of those books that a pain to read, but afterwards you're happy you did.

Although I'm dyslexic, so everything is a pain to read.

If you want to read a morally grey white savior story with boring purple prose (I like purple prose!), nonsensical politics, and lazy orientalist worldbuilding go ahead

Oh also the incest

EDIT: oh lmao I thought you meant frank. no don't even consider the fanfictiony ones

Yes, though the level is very varying, Houses and Great Schools trilogies being quite good imo while the Heroes trilogy is, mildly speaking, bad.
There's also the Butlerian Jihad trilogy which flatten the forming event of entire setting from complicated philosophical and military conflict in which bad guys won and crippled humanity for possibly forever into an ordinary survival war against Skynet.
Or the Caladan trilogy which is honestly quite good but while it ends when the orginal Dune starts, somehow it ends up with political situation being 180 from what it should be for the original plot to happen.
And finally, there is of course the two book ending of the original cycle, which i read many times and now i'm convinced Brian didn't lie about finding the Frank stash, the books are way more similar to the original Dune books 5-6 than to rest of Brian's books (this isn't much of a compliment btw, i consider Heretics and Chapterhouse the weakest parts of original).

The few that I've read are, quite literally, the only books I've considered burning.

I even gave KJA a sporting chance and read his seven book Saga of Seven Suns.

Garbage.

This is, of course, only my opinion. People are allowed to like different things.

No.

I only went to Wikipedia after I posed this question. I honestly did not know that he had done prequels and side stories. I thought they were all followups. Also he was pushing out one a year? That can't be good. I might start with the last ones assuming he's found his stride by then. So library it is.

eta: I also consider the last two books to be the weakest. He could have ended it after GEoD and it would have been a solid series.

Actually only 2 books are follow ups, 3 are in between of Dune and Messiah and rest are prequels, plus iirc one book of stories, that one about Gurney was quite fun. One book per year is nothing out of ordinary nowadays, that's how the publishing houses crunch authors, hell even for example Terry Pratchett was churning 1-4 books per year for most of his career. Also idk how they are dividing the work, but i would imagine most of actual writing is done by Kevin Anderson since he was a real deal crunch writer even before starting cooperation with Brian, there's two of them.
Oh and also look for the 3 volumes graphical novel of first Dune book by Raul Allen and Patricia Martin. It was directed by Brian and it is seriously the most faithful adaptation of the book ever made.

You can read it. It won't be Dune, but you can read it.

I did read the house prequels some time ago and they were not unreadable, but still a far cry away from real Dune.

Since you've apparently started reading the expanded universe sequels I should just say (trying to avoid spoilers as much as possible) their idea of what was the "final enemy" of Dune is not at all what was suggested in Frank Herbert's works, and apparently requires reading their Butlerian Jihad prequels (which likewise aren't anything like how the Jihad was portrayed by in the actual Dune series).