Its basically D&D 3.5 but with a lot of updates that make it make more sense. 4.0 kinda changed the direction of the game and a lot of people didn't like it so people who liked 3.5 better made pathfinder.
Keep in mind that "make more sense" is strongly subjective. While they did improve things, like making the rules for special combat moves like grapple and disarm easier to remember, or trying to favor single-classing with different rules for cross-class skills and no "i get nothing new" levels... magic users have more than just spellcasting now and mundane characters get a few more tricks but they still don't equal spellcasters. (Some say the difference between full-casters and mundane charachters is wider now.)