I just read the first two books and I'm working through Children. Honestly, I'm not that impressed. Dune was a pretty paper thin story, and the plotting of the various characters isn't very deep. The book expends a lot of words to say the characters are brilliant tacticians, but their plans aren't very sophisticated and victory usually comes from the enemy fucking up. Dr. Yueh is supposed to be an incorruptible graduate of the Imperial school of unbreakable conditioning, but all it takes to corrupt him is torturing his wife. The Atredes are brought down not by careful plotting, but by underestimating how much money the harkonens were willing to spend to destroy them.

Dune Messiah has no plot that I can tell. Nothing happens, nobody's scheming achieves anything. Nothing is accomplished, then everyone dies.

The books have been enjoyable, but I haven't found them satisfying and I probably won't continue past Children.