Frank Hebert is a magnificent world builder, and a sci-fi author that really thrives off of concepts and the development of ideas and philosophies. However, his prose and his characters are not all that great - so in that sense, he's very much a classic sci-fi writer.
I personally love sci-fi that focuses on ideas and concepts, and find Herbert's philosophizing about the future of humanity and its relationship to technology, spirituality, and politics really fascinating (and impressive, just the sheer amount of vision and creativity he possessed). I've read them all multiple times (they're dense and possess a lot of depth). Also, its good to take into account that the series spreads across massive amounts of time, and unlike other series, plot-wise each book doesn't necessarily have a direct or immediate connection to the books before it (once again, he focuses on history and development, sort of like an annales school approach - albeit mixed with a bit of a "great man" approach too).
So if you're looking for closure with characters from the first book, you're not necessarily going to get it. And Frank Herbert ultimately died before he was able to fully realize everything. So yeah, it really just depends on what you're into and what interests you.