mechanics
weight, walkspeed locked to physical strenght, limited bags (inventory), diversity, character customization, self-actualization (the of-use feeling), a properly working economy, ecology, aging, decaying of food supplies, sustenance, corrosion of gear locked to environmental humidity, no instant repairs, no overpoweredness but realistic limit breaking, proper graphics, social neccessities (sims/mabinogi)
a game is supposed to take time, thats why most mmorpgs dont really surpass the 5 year lifetime mark in being successful