He is tough as hell
Brett has started in 261 straight games including the playoffs. In the NFL that is a phemonenal achievement that is only accomplished by playing with severe injuries taht would sideline a less tough player. Brett has started every game since his first start in 1992. Only one other player (Jeff Fegales, a punter) can claim this honor over the same period.
He plays with the same joy of a little kid
At 38 years old, he might be the most pumped up guy on the field. Although there are lots of high energy guys, Its hard to find many people as charismatic as Brett in the NFL.
He has won a Super Bowl
He's led his team to two Big Games and won Super Bowl XXI against the Patriots.
He is human
Brett Favre checked into rehab for addiction to pain killers and alcohol back in 1996. Superheros with flaws make them that much better.
He keeps coming back
I have to admit after the last two years I was hoping he would hang up the cleats. It's awful to see someone play like a shell of their former selves.
But this year it's like old times. He's slinging the ball around and is genuinely hooked up to the rejuvenation machine. How much easier would it have been for him to decide enough is enough?