I have the same quibbles about this book as I have about the Probability Theory book of Sheldon Ross. The chapters are just too large, there have to be some more smaller easier exercises sprinkled in between them, especially considering its just an introduction text to the subject. It's just extremely difficult (at least for me) to grasp the concepts properly if I cannot test myself often enough.
Granted, I didn't finish the book, I finished 6/11 chapters, I may come back to the book if I need to. Its the only book I know that discusses various probability models, though one might be better of just studying books specifically talking about a certain probability model, like Queuing theory, or Markov Chains.