It's a good deal.
Wall is still very young and if he can stay healthy has shown the ability to be a mix of Rondo and Derrick Rose.
It wouldn't shock me if Wall leads the Wizards to the playoffs this season while averaging 18+ pts, 8+ ast, 4+ reb and 1.5+ stls.
Barring any major injuries he'll be a threat to do that every year for a while.