Garth Ennis’ John Constantine: Hellblazer is supposed to be totally awesome, but it’s absolutely not. It’s a remarkably flat story, with a basically uninteresting plot and no characterization to speak of. There’s a Keanu Reeves movie based on this book, and the movie is much, much better (and has a better plot resolution). See that instead. (Do latter Constantine books get any better? I’m vaguely interested in reading them, but not if they stay this dull.)
Garth Ennis’ Ghost Rider: The Road to Damnation is not bettered by a movie, but only because 1) the Ghost Rider movie isn’t out yet, and 2) it has Nicolas Cage in it, so will suck. Otherwise, it almost certainly would be, as it’s a boring story that struggles to fit Ghost Rider into it, and essentially fails. This is less Ghost Rider and more Eternal Struggle Between Heaven and Hell, Guest-Starring Ghost Rider; it could easily be part of the same universe as the Constantine book. There’s no reason at all to read it.
On the basis of these two books, I have to believe that Garth Ennis is a talentless hack, and that people who’ve said he’s a good writer are insane crazy people. I’m deliberately not seeking out anything else of his.