They're FUN! Not highly competitive, but challenging enough for those of us who aren't raising "elite" athletes. The fact that it requires only a weekly commitment allows my kids to be involved in other activities as well.
I appreciate the focus on FUNdamentals and sportsmanship. I'm a pretty competitive guy, but at ages 3-5 (my kids' ages) this isn't the Super Bowl/World Series/World Cup/etc and we could use more places that teach the fundamentals well without burning out kids or making them feel like a failure if they drop a ball at age 4.
I like that the practice and game are on the same day. I like that it's a program that promotes healthy competition, and that there's a great deal of positive that comes with the participation. I also like that it's a flag football league, thereby minimizing the risk of injury due to contact, while still allowing for a significant amount of physical activity.