I generally side with players in most issues, but at this point, they shouldn't be able to sue the NFL for this anymore. This recent generation of players now have all the information available to them and it's practically common knowledge what repeated impact to the head does to the brain. Older players didn't have that info and the NFL straight lied to them about it. They have a case. Now, you either accept the risks or don't play.
Players now should not be able to sue the NFL and should have to sign a waiver releasing the NFL of all responsibility for such issues. At the same token, the NFL should have better plans in place for taking care of their players after their careers are over.