Something I've been thinking about recently...
Gamestop functions on a system where people sell back games so Gamestop can then sell those games as used, generating 100% profit for Gamestop and completely cutting the publisher out of selling a new copy of the game. It's quite ingenious. It allows people to spend less money to get the games they want while simultaneously allowing Gamestop to sell the same copy of a game 3, 5, maybe even 10 times over.
There's one key lesson publishers need to understand in all this: if you don't give gamers a compelling reason to keep your game, then you're going to get screwed out of many, many potential sales, not just in terms of Gamestop, but in rentals, resales, borrowing, etc.
To date, the most compelling reason is a multiplayer mode, but even better is an ONLINE multiplayer mode. It's a simple equation: the more gamers keep your game for a longer period of time, the more gamers will buy new copies instead of finding used ones.
To the point, which will have a higher percentage of used copies show up at a local Gamestop, Metroid Prime 3 or Halo 3?
This is one of the reasons Nintendo's stubbornness in embracing online gaming irks me so much: first day sales are going to be weaker for games which most players know will show up used in less than a week if they're willing to be patient. Halo 3 didn't suffer this stigma because most players are buying it for the multiplayer and thus will keep the game for a while after purchase, unlike MP3 which players will complete and likely sell back for store credit toward Mario Galaxy, which they'll also sell back for store credit for SSBB which they'll probably hold onto for a while because it has online multiplayer.
We don't live in a market paradigm where getting a game sold is the end of the battle. Games are a volatile commodity, as the trade in credit for a particular game will go down after time, urging players to beat a game quickly and sell it back quickly. The trick is giving gamers a valid reason to not bring it back to Gamestop.
It'll be interesting to see how many copies of SSBB show up used a week later...