To be honest, I think it was all the secret loot. I love exploring secrets and Risen 3 is full of treasure that hides off the beaten path.
I enjoyed Elex enough to play it again eventually. I just didn't care for the mixture or sci-fi and fantasy. Elex has a lot of hidden loot too, but most of it is just coins or something similar. In Risen 3, the loot made a difference. In Elex, most of it is not game changing and I need to be rewarded for my exploration.
My favorite battle in Elex happens in the first few hours. There is a camp of bandits with a wandering troll nearby. I loved trying to kill both groups with the stuff you can find around that area. I can't remember if it's grenades or what, but that was an amazing fight. Once I started doing the quests, I just got bored to death. I didn't want to join any camps, I wanted to kill everyone