With that said, I feel like Diablo II and World of Warcraft manage to be devastatingly addictive without feeling very rewarding—for me, at least—simply because Blizzard designed them only to stimulate the ever-loving crap out of the human brain's reward center. When I play Diablo II, I am rewarded for my tireless, ceaseless clicking. I play a fairly popular mod called Eastern Sun (a friend admonishes me constantly for this, saying he thinks vanilla Diablo II is better), and with the tweaked drop rate and vastly increased number of uniques, set items, and so on, I get to see all kinds of new and exciting gear. Goals are set for which items to grind or gamble for, what level to hit, and so on.
By the time all is said and done, though, I may have bumped up a couple of levels and amassed a veritable wealth of gear, but nothing has actually happened. Even in the game, progress doesn't seem that exciting. The story itself never struck me as being terribly compelling, crippled by how orderly the game plays out. I never really feel like I'm getting anywhere, knowing I'll just be playing the same five acts on a harder and then harder-still difficulty level.