You could possibly get in on one of the coolest promotions I have seen a game company run. http://community.darksiders.com/ Check out the "Mystery Code Revealed" Entry. That should be what the Mystery Code sheet looks like. What it gets you is: Spoiler -Red Faction: Guerrilla for PS3 or 360 at the cost of shipping ($5) - Digital Hellbook Disk full of concept art and other stuff related to Darksiders
I got it to work a few hours ago. I'm not having any trouble right now either, on firefox. The deal is good until like march 12th. So people who don't have darksiders yet might be able to take advantage too. I think it's $40 at gamestop right now. So you could conceivably get darksiders and rf:g for about $50 (after tax/shipping).
I only have experience with RF:G, but it's tons of fun. Plus, it's $5! Surely you could sell it to someone for that if you don't like it.