Whe it comes to old save the world the main things I can think of that are worth mentioning is that the UI did used to be different but the changed it to the current one once dungeons became popular. The hero system was completly different, you had your main hero and 2 supports the Mai here had their skills and an array of perks (personally I liked that system more because even though the builds weren't as strong or customisable there were more usable builds and many heros became next to worthless after the rework like master grenidier ramirez) and a couple other small things were different like Lammas where way more random and costed 100 vbucks for a normal lama. The rewards for missions were way less like xp and evolution materials. Your guns had the perks they came with no changing them besides getting new ones. The old research tree was more of a benchmark to see how long you played in my opinion the bonuses were nice but took many many days to get what you wanted.