I own some books from Packt Publishing and they are not bad. Of course, each book is different from each other, and some are better than the others. But that is normal that a publishing company that is trying to gain space in the market with serious competitors (like O’Reilly, Apress or Manning) needs to publish a lot, making it more difficult to publish good quality books.
But after having a few of them, my main complain is not regarding the book contents, but the book design. It seems that Packt responsible people does not know typography nor marketing.
Regarding marketing: try to make your books similar. Not only the cover, that you are already doing, but the inside too. They are not very different, but they are different enough to be a pain to read some of them, while other are pleasant to read.
Regarding typography: accordingly with the table of contents of the books I am able to understand there is a chapter level and, inside each chapter, a section and subsection level. But unfortunately, when reading the book, the titles for sections and subsections are similar. If they have some difference, it should be one millimeter or so. That makes reading the book very difficult. The reader never knows if the subject is continuing or changing. You do not need to add numbers to the section and subsection titles, if you do not like them. But change the style! Make one of the titles underlined, or italic, or gray, or something!
Oh, and finally, try to convince authors to make a good index. If your book is in a programming language, or a library, and examples use a specific keyword or function, please add it to the index, and point to the page where it is explained. That’s how users want to consult the index, not looking for the name of the example application.