Sessegnon has completed a three-match ban for his red card at Newcastle earlier this month and is a certain starter to face QPR at the Stadium of Light.
"He's frustrating at times, like all players of his type can be," said O'Neill, whose side are looking to bounce back from their midweek defeat at Blackburn.
"But he's got something special that teams love to have.
"Sess will try something different and lose it and try something else and lose it again.
"But then suddenly he can just completely open up a defence and you can have two or three good goalscoring opportunities."