Actually Paranoia 7 is the most current. Probably the biggest difference is there are three styles of play. Zap, Classic, and Straight. Zap is a free-for-all and you'll surely end with no clones left. Classic is like 2nd. Straight is closer to an RPG where you investigate and survive. A more gritty multi-session game.
There are rule refinements and cleanup.
Oh and they dropped all the punny names although the reprints have them listed in the back generally.