Zambrano posted his best ERA as a starter last season at 4.17 as well as his lowest walk rate at a gaudy 4.17 BB/9, but he also posted his lowest strikeout rate at 6.06 K/9 and his highest hit rate at 9.20 H/9. He is frustrating to watch, alternating solid starts with terrible ones, allowing far too many baserunners and taxing the bullpen. He averaged fewer than six innings per start (5.98), and his peripherals suggest that he is actually worse than his ERA might have you believe.
I am not a Victor Zambrano fan, and I would be perfectly happy just letting him fade away into oblivion on some other team's roster. He is a mediocre pitcher with natural ability but terrible mechanics and I have no reason to believe that he will ever be an above-average big league pitcher, or even a consistently-mediocre one. He is not an awful pitcher, and is probably worth the $3 million the Mets will pay him this year, but the Mets would be wise to keep him on a short leash. Should he struggle early on as a starter (assuming that's where he slots in) the Mets should waste no time in banishing him to the bullpen or to Triple-A and replacing him with someone like Brian Bannister.