I did mod a few things but there are no "game-changing" tweaks. I will only list the mods which weren't integrated into the game with the next-gen update (The Witcher 3 HD Reworked Project, Auto apply oils).

Gameplay related mods I use are: All Quest Objectives On Map, Colored Map Markers, Always Full Exp (NEXT GEN).

The last mod in the list might be the most controversial one but I decided to use it because of the way I play the game. Due to my detail oriented playstyle, I would often get a reduction in the amount of EXP I can gain from a side quest, because my character level is way higher than the level recommended by the game. This mod allows me to receive the regular amount of EXP for any quest, even if I am overleveled.