Fossum has always had a decent amount of talent. He's a lefty who works in the low 90's and has a big breaking curveball. He strikes out a good number of batters. His problem has always been developing a third pitch and consistently getting his curve over.
I haven't been so surprised to see him succeed lately, I've always thought that at some point he could become a solid starter and, with those K's, a good fantasy option. I agree with the other poster who said he'll get better with age. I can see that happening and I think he'll be a good value next year because he has shown some good flashes this year and because ...
... He's about to have a really rough last two months. As was also pointed out above, the Rays have a brutal schedule to finish the year and Fossum has the worst of it. He basically has the Red Sox, Yankees, Rangers, and O's the whole rest of the way. I was about to pick him up in a deep league where he was clearly the best available starter and then I checked his schedule and realized he is unstartable for 90% of his remaining chances.
Look to take a cheap chance on him next year.