Writing On the Board vs. Showing Slides
What you describe is not teaching with slides, it is teaching very badly with slides.  A teacher can teach very badly with the board too: as an undergraduate, I had one mathematics professor who only mumbled inaudibly while either facing at an oblique angle to the class or else while writing small unintelligible letters on the chalkboard in a descending arc.

Slides can be an excellent teaching tool, in that they allow a professor to show images, data, illustrations, and other things that cannot be readily drawn by hand.  I find that their main disadvantage is that they are fixed before the class, and thus cannot be readily adjusted or corrected to track the interaction with students on the fly.  Conversely, working on the board can be more interactive, but must remain much simpler, which can be either a good or a bad thing, depending on content.