Welcome to Chrons, and thanks for joining in the discussion.
You have picked 4 quite polarising books, and I can understand why people might find any of them disappointing, which is not the same thing as saying they are bad, as such.
My view on these:
Dune: Good book, clearly an important part of the canon. A bit portentous in places. I enjoyed it less as an adult than as a 12 year old. Did not enjoy any of the sequels.
The Stars My Destination: Brilliant. Just brilliant. Blew me away as a teenager, and I still love it decades later.
BOTNS: Likewise. The first book especially. Can be heavy going in places, and it is wilfully obscure. but well worth it.
Behold the Man: I think this is mainly a piece of deliberate provocation rather than anything very profound. Like a lot of New Wave really. I think Moorcock is really interesting and I have read most of his published works. This is not my favourite of his. Try Breakfast in the Ruins for comparison, but for his most arch NW go for The Final Programme.