Zambrano was overrated for years IMO, even the years he was considered a fantasy ace. Now I think it has swung the other way around and this year I am finally owning him in some leagues. Just last night I took him with pick #173 and couldn't be happier.
In a "down year" Z had a 3.77 ERA and a 1.38 whip along with 8.1 K/9. Not great and definitely not an ace, but not too bad either. If you take out his first outings after his two DL trips (and I would never start a mid-tier pitcher like Z right after he came off the DL) he had a 3.37 ERA, a 1.35 WHIP and 7.9 K/9. That's not "he sucks" territory.
His WHIP isn't great, but he is a career 1.30 WHIP guy and he's been hovering above and below that the past few years. Again that's not great but it isn't a single-handedly killing your WHIP guy. He's a guy that's been under a 4 ERA each year for the past 8 years, which not many guys can say that - not Carpenter, Sabathia, Hernandez, Haren, or Halladay to name a few.
It's easy to bag on Z because he has very little upside, has such big-name recognition and has been over-hyped for so long. But he isn't a bad pitcher for fantasy when you can get him around the time others are taking Slowey and Wolf types.