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
Bookmarks