Sort:  

The newest two - Origins and Odyssey - turned the franchise into more of an RPG. Origins added gear management and skill trees, and Odyssey improved on those and added in dialogue trees where decisions have a lasting impact on the game. Both also make the game less of a 'press X to kill' auto kill feature, making it so that you could very easily die, even on normal mode, by being too quick to act and not paying attention.