Why is WoW successful? (1) They started with the successful and highly addictive Everquest format. (2) They used a small number of classes, carefully and crea

Why is WoW successful? (1) They started with the successful and highly addictive Everquest format. (2) They used a small number of classes, carefully and creatively allocating abilities to each one in order to make that class fun to play: either solo or in a group. They also tweaked the mana/melee balance to be more flexible and interesting and combat was generally faster paced than in other MMORPGs. (3) They set the bar for failure lower, and the penalty for failure was less punishing. This encouraged less-hardcore players to experiment more and try different things, rather than always sticking to the safest tactic. (4) They designed for PvP from the start. (2) + (3) + (4) = Replayability. People log in to play WoW because it's fun to play not just because they want to hit the next level. (5) They used frequent, incremental rewards so that players logged out always having felt as if they accomplished something. (6) They started with a huge Warcraft fanbase, and marketed to their audience with hip, exiting videos and information. (7) They kept system requirements LOW. They focused on getting realism through animations and colorful symbolism rather than high poly counts. They avoided the "uncanny valley" of character models while delivering a game that players could play on the hardware they already owned. (8) They marketed the game worldwide. (9) The game loads quickly, once it's patched. You can decide you want to play WoW and be online in a minute or so. (Others may be better now, but when WoW came out EQ took 5-10 minutes from desktop to spawning in-game) (10) Instanced content made it easy to avoid the more annoying social aspects of an MMORPG. Fighting for spawns was fun in EQ, but that's not needed in WoW because the combat engine is better.