I think it's become something of a myth that Ebert didn't like horror movies. He gave a highly positive review to The Last House on the Left, for cryin' out loud. The list of horror titles that he reviewed favorably would be massive, but here are a few off the top of my head: Halloween, Dawn of the Dead (he liked both the original and the remake, but he gave the original a perfect score), Re-Animator, Henry: Portrait of a Serial Killer, The Devil's Rejects, The Cabin in the Woods...
He just didn't like mindless body count movies, and there's nothing inherently wrong with that. Maybe his crusade against slasher movies was a bit much, but I can't knock the guy in general for demanding more out of movies.