's rarely as entertaining as it could have been 
(ROOT (S (VP (VBZ 's) (ADVP (RB rarely)) (ADJP (ADJP (RB as) (JJ entertaining)) (SBAR (IN as) (S (NP (PRP it)) (VP (MD could) (VP (VB have) (VP (VBN been))))))))))
(ROOT (S (VP (VBZ ) (ADVP (RB )) (ADJP (ADJP (RB ) (JJ )) (SBAR (IN ) (S (NP (PRP )) (VP (MD ) (VP (VB ) (VP (VBN ))))))))))