As a professor who is in charge of selecting books for my courses at a very reputable institution, I have to say that I am very disappointed.
The main difference between the 3rd and 4th edition is that someone who is obviously very good at composition (but knows little or nothing about Matlab) has spent an extensive amount of time combing through the entire document to create a pristine-sounding, professional textbook. That person did a good job at his/her given task, and if that is your style preference, you will appreciate the 4th edition. I actually appreciated the casual tone of the 3rd edition, myself.
However, the content is *identical*.
And by identical, I mean, this includes any errors in the 3rd edition. For example, I was desperately hoping that if a new edition of this text were to be published, that someone would correct the issues in Chapter 13 (GUIs) due to the fact that Matlab no longer acts the way it used to. For example, p.295 (3rd edition) p. 266 (4th edition), the statement
disp('pushbutton1 Callback not implemented yet.')
is actually no longer auto-generated. Neither does the "varargout =" show up in the autogenerated code. On p.298/268 it says you need to select Tools, then "Application Options", when you need to in fact select Tools and then "GUI Options".
One of the most common requests I get from my best students is that they want to learn GUIs. I cannot recommend that they read ahead in the text, and in fact I am not even going to require the text, due to excessive issues of this sort. All I can tell them is to wait until we get to that topic in class, which may be the following semester!
Another issue I have is that much of the artwork appears to have been cheaply scanned from a paper copy of the old edition. These diagrams are fuzzy and hard to read in the new edition. It would not have taken too much extra effort to regenerate the screen captures.
My unsolicited advice: If you are going to create a new edition of a textbook for Engineers, next time, I would suggest you hire an Engineering graduate student rather than an English Literature graduate student, to go through the entire document for accuracy rather than adherence to grammatical standards. The improved language will do nothing to help your readers with the accuracy issues.