I am a newcomer to the Realms and, relative your experience, a newcomer to D&D in general.
First, specific to your request, there are few game rules compared to the 3.0 setting. This is much as another poster said earlier.
I like this treatment of the setting a lot. While I had access to the 3.0 setting, I could never get into it because I felt the setting had too much baggage for me to run comfortably. This version, however, feels like a fresh start. I'd like to run it as soon as I can talk my group into playing.
Also, the PoL gives a sense of dynamic feel to areas that previously felt staid, like Cormyr, Sembia, The Dalelands, and Luskan. Complementing these are areas like Waterdeep, the Silver Marches, and Baldur's Gate, which serve as stable and relatively unchanged homes for the Player Characters.
Finally, I'd be wary of the immense volume of negative reviews. They don't accurately reflect the book.
First, you don't know how many actually read the book vs. the .pdf. I downloaded the .pdf and found the book tiresome and hackneyed, but when I sat down with a physical copy at my FLGS I was very impressed. Give the book (not a .pdf) a chance.
Second, as the OP correctly surmised, large numbers of older fans don't like the book for various reasons. These constitute the largest part of the book's detractors, yet statistically most people who write reviews have strong feelings, and most disapprove of the thing in question.
Personally, I think these people are entitled to think what they what, but the cacophony of their objection robs a potential buyer of the balanced view and might give and unjustified bad opinion of what I think is an excellent book.