I've played lol, dota, l2, wow, aion, cod, hon, rift, terra, blade and soul, guild wars, metin, moh, cs, s4 league... Anyway, I've played all games.
I can safely say that L2 is the hardest game ever created and takes more skill to play than any other game. At lol you just kill some towers and win the game lol. That's damn easy. In L2 you have to farm, exp, pvp, craft, siege, buy potions from the shops, teleport using Gatekeepers, learn skills from NPCs and be hero. So hard...