Very similar. But many small things have changed. Which means you still need to read through almost nearly the entire thing... expect it to take awhile to get caught up on that huge book. If you like 3rd and not 4th its a nice change. But if you like 3rd and already have 3.xe books...well there's not really a huge reason to change. You can update 3.xe books to pathfinder but its annoying. Summary: overall probably an improvement, but its not worth the cost to many.