Here's mine for an MMO RPG:

World like Skyrim

Economy like Ultima Online

User-generated buildings/caves/tunnels/etc like Minecraft (with appropriate costs for tools/"dig permits"/etc to make the cost of a player-built house comparable to purchasing from NPC)

Player population of World of Warcraft

Big-ass map (computer-generated for be nearly infinite like Minecraft?) with some kind of way to get around quicker like mark/recall or gates.

Weapons and Magic

Integrated web browser

Many options for avatar design