Obviously we're never going to see Nene at full health ever again. His planar fasciitis means that he is always either hurt, on minutes restriction, or working himself back into 100% shape (before irritating his foot again).
But, since he's been in the league so long, we have a pretty accurate picture of what a healthy Nene can do. He ran one of the fastest full-court sprints in combine history for a center (3.19 seconds). The only guys to beat that time and actually be successful NBA players: Dwight, Emeka Okafor, Cody Zeller. At his size, that means he's one hell of an athlete.
He's a 260lb physical beast with huge hands. He's a willing and creative passer. He has legit post moves and counters, and he's extremely efficient in the post. His spin moves and dunks
His biggest weakness on offense is that he's only an average shooter for his position.
His impact almost makes you want to sit him most of the regular season to have him fresh for the playoffs. I'd say a rested and healthy Nene is a top-5 C in the league.