I love to read mysteries from the '30s and '40s and loathe most of the modern stuff. Christie was probably the best, though my personal preference is John Dickson Carr. If you're a serious fan of mysteries in general, I suggest getting a copy of A Catalogue of Crime, by Barzun and Taylor, to use as a guide.
I beg to differ with you, though, on not thinking too hard while reading them. The best "play fair," so reading the progression of the story becomes a game of wits between you and the author. Then again, I think I know what you mean. The hours spent reading them is an "escape" that is quite relaxing, or something, and I have consumed a ton of pipe tobacco while so engaged.