even if the top-billed willis is not the most impressive player 
(ROOT (SBAR (ADVP (RB even)) (IN if) (S (NP (DT the) (ADJP (NN top) (HYPH -) (VBN billed)) (NN willis)) (VP (VBZ is) (RB not) (NP (DT the) (ADJP (RBS most) (JJ impressive)) (NN player))))))
(ROOT (SBAR (ADVP (RB )) (IN ) (S (NP (DT ) (ADJP (NN ) (HYPH ) (VBN )) (NN )) (VP (VBZ ) (RB ) (NP (DT ) (ADJP (RBS ) (JJ )) (NN ))))))