The basic fact that Odin is a fucking bad ass and you totally want him to be your God. The dude has one eye, was impailed by his spear for 9 days, and he has fucking ravens as pets...seriously? How much more bad ass can you get? The religion is based off the sole fact of screaming loudly and epically into the sky (while shaking your fists) to Odin for whatever you want. (Usually weather realated.)
Example of Odinism at work:
Greg: "Dude, Odin isn't real."
Jordan: "Oh yeah? (While shaking fists to sky) ODIN BRING FORTH A RAIN STORM!"
*later that day at a football game*
Greg: "Holy shit it's fucking raining like crazy!"
Jordan: "Damn straight."