Authenticity - can't argue too much. I do think All-Pro Football 2k8 feels authentic in its representation of t he game of football. The little things add up to a monumental difference. This could also qualify in gameplay.
Fun - Tecmo Super Bowl for the NES takes the cake for me. This game is fun. Simple as that. I never get sick of it.
Personally I think more developers should treat dynasty modes more like RPG's. I want abilities over numbers - and random events for me to overcome that emulate real life. Can't tell you how many times I've pandered for abilities over numbers. 2k has it right here.
Just throwing my opinions out there. I don't post enough on OS anymore