A big change was 1E gave out less XP for killing monsters and had the bulk of come from gaining treasure.
2E boosted XP for monsters, pushed the notion of story awards and made XP for treasure optional {IIRC it was even suggested against doing so].
This change turned wandering monsters from high risk & low return to be avoided [1E] to Wandering XP [2E].
I fell in love with the Conan RPG XP system. The rule is: There are no rules. It's completely up to the GM.
The GM awards points, as many or as few as he thinks should be awarded, on whatever he thinks is important to the game.
What was important to the gaming session? Was it a story goal that the players achieved? Was it some outstanding roleplaying? Was it a particular fight? Was it a particular discovery?
The Conan GM is encouraged to use XP to reward player actions that make the game fun to play.
So, on one game session, a character may be instrumental in taking out a large Vanir warrior that attacked the camp. He may get a lot of XP for that. Then, next game session, he's one of many, PCs and NPCs, who fight in a large battle against the Vanirman's clan. Even though the PC got a lot of XP for killing the one Vanirman last game session, and the same PC has killed four other Vanirmen this session, that may not be what's important to the game that session--and the PC could end up getting less XP for the four kills than he did for the one kill.
Again, it's about encouraging the good things that happen in the game, and it's 100% up to the GM's opinion about how these points should be awarded and in what amounts.
I really like the system--more more than I like the regulated XP systems of the various D&D editions.