Palmer has played as many hoped he would following last year's torn ACL. The Cardinals passing game has fired on all cylinders this season, and Larry Fitzgerald has risen like a Phoenix (alright, I admit it, the pun was intended).
But with all that being said, Arizona has beat up on some pretty bad defenses so far (New Orleans, Chicago and San Francisco). This week the Cardinals draw the Rams and their fearsome front four. While the St. Louis D plays better at home, I think they will still be a force since the game is indoors on a relatively "fast track".
Palmer isn't the most mobile quarterback in the league, and could struggle staying comfortable in the pocket against the fierce Rams pass rush. I would not expect things to be as easy as they have been for Palmer and the Cardinals the first three weeks.