I actually don't mod games all that often, because I usually only want mods that either add content seamlessly, improve graphics/sounds or fix some obvious problems with the base game. For example, I wouldn't even think about playing Skyrim without SkyUI, but I don't want a witcher armor set or whatever the fuck. There are remarkably few mods that bring content without feeling completely out of place, but those that do (there was that collection of well-written quests for Skyrim) are awesome.