I missed this a couple months ago and just saw it. Roger Ebert lists a whole bunch of guidelines to which he believes film critics should adhere. Some of them seem like deliberate swipes at specific colleagues, especially Ben Lyons, but that doesn't mean they aren't all (or nearly all) valid.
One that jumped out at me was…
Trailers. Have nothing to do with them. Gene Siskel hated them so much he would stand outside a theater until they were over. If he was already seated in the middle of a crowded theater, he would
shout "fire!"plug his ears and stare at the floor. Trailers love to spoil all the best gags in a comedy, hint at plot twists in a thriller, and make every film, however dire, look upbeat…
I sometimes feel that way about trailers…but for all the same reasons, I sometimes felt that way about watching Siskel and Ebert review a film, spoil all the best gags in a comedy, describe plot twists and show us some of the same clips that were in the trailer.