Dune is very much interplanetary, though. Almost no time is spend on space ships and much of the story is shown from the perspective of characters mostly stuck to one planet, but the story as a whole is all about events that happen on different planets at the same time. Even the first book has things that happen on the Artreides planet, on Dune, on the Harkonen planet, and on the Emperor's planet. And they are not separate plotlines running in paralel, but the same struggle.
The reason that I think Stargate doesn't feel like Space Opera is that it's about contemporary humans who never really leave Earth behind to become part of a greater world. They use contemporary technology and the people they meet are also humans or effectively demon-possessed humans. They never take the "first step into a greater world". It feels more like an alien invasion story in which most of the fighting takes place on the doorsteps of Earth than actually Earth itself. Though I know that later in the series they do introduce all kinds of space ships.
Another thing I've seen described as space opera but really doesn't feel like it to me are the Riddick movies. Which I really quite like as the B-Movies they are. Again, they don't feel like there exists a greater universe beyond the horizon. I only recall one intelligent alien and that one took on a normal human appearance. There is some space magic and the conquerors in the second movie have very big and stylish ships, but the setting does not have the feel of a great scope and alien worlds.
Same thing also with The Expanse, but I only know that story up to getting access to the gates. It might change after that.
