Overrated?
It's funny, but sometimes I wonder if it's true that people highly rate movies they're *supposed to* like.
I know that sounds like anti-elitism knee-jerking,... but I guess my main feeling is that people appear to be willing to make allowances for dated directing, acting, and technique in general.
I'll start with probably the most obvious issue in Strangers on a Train; the acting.
The acting here fell into a few categories.
It seems that when it came to old lady characters, Hitchcock went for something that was basically an upgraded Margaret Dumont thing; stage-style, classically executed hamminess. These ladies were masters of stage farce, and I could see that they were willing to step into dark areas at Hitchcock's behest--and that reflects a kind of admirable professionalism--but in the end you saw a screen acting style that I don't think has aged well.
Another acting issue was the occasional bad actor. Face it: Farley Granger, bless his heart, wouldn't be tolerated for a second in a contemporary movie; even if he had twice the good looks, he still wouldn't get a part. Modern casting is supremely picky. Casting directors sniff out the smallest margins of non-talent, precisely so the audience won't have to smell it. There are venues for pop fare with lousy acting, but it's reasonable to hold Hitchcock to a higher standard. Farley let's his character slip/go wooden often enough that it's obvious he wouldn't make the grade these days.
Another factor is that, for all of Hitchcock's reputation as a filmmaker who broke with convention in a way that could attract more discriminating audiences, I've recently noticed a set of stock elements in his films, and it grated me a little to see it here: A basically good-hearted, but compromised male hero, led to redemption by a beautiful, good-hearted gal. And these Hitchcock redeemer women are cast and directed pretty much the same; knockout beauties with eyes ready to go filmy at the least provocation.
Another stock element: Law enforcement issues are tidied up so easily it almost looks flippant.
All that said, there are still things to recommend Hitchcock, of course. But think about these issues. And please add some of your own!