I find if a game's leveling or customization system is too complex, I get a bit overwhelmed. I'm not a fan of being asked to level a character manually with a whole bunch of stats that are unclearly explained without an online FAQ. If a game is challenging, that's one thing, but if you're unclear of what you're doing without researching the best way to level up, that's another. I can understand how people might have fun experimenting with those types of systems, but I'm probably not one of those people.