On the subject of Ebert and Roeper, first off, I loathe Roeper. His worth as a film critic is negligible.
As for Ebert, I found his early writing interesting and informed. He loved film and was able to write about it intensely. But by the time he became a "star reviewer" on TV, particularly after he and Siskel left PBS for their own syndicated show, he seemed to lose his edge and his standards just went into the toilet. Since his brain operation, he doesn't seem to have many critical standards at all any more. He seems to like almost everything studio produced. I'd hate to say he's sold out to the big studios, but that's what it seems like.
Siskel was a political reporter who was assigned to the movie beat when the Chicago Tribute lost their first string critic. He never had any opinion that I felt was worthy of a second glance. (I remember he panned SLEEPING BEAUTY saying the animation was flat and uninspired. See? Worthless.)