Manning - one of the all times greats with a bad neck joining a stacked team as the final piece.
Flacco - a QB who had moderate to good success with a bad neck joining a not so good team as a 2nd or third stringer.
Most on this board are Bills fans so it is hard to pick an underrated player among us. Nationally I'd say Brown, Hyde, and Allen are the most underrated but Allen has people who love him. The ones hating him are relentless and over the top.
@GunnerBill has covered a lot of this in a fair amount of detail. Take a look. Edmunds plays a critical role in our defense, which is rated very highly.
I understand he is highly regarded on this board but so are most players. The national media generally says good things during games but hardly mentions him at all when listing top players. I just don't see how he is overrated. He is most certainly a better player than Milano. That is no knock on Milano.