The film was highly entertaining - even when it went a little crazy in the end, being somewhat unrealistic. But I didn't mind as I bought into all of the action. Some of the set-ups were just a tiny bit too obvious, such as the writing on the window. But then again, maybe it was exactly what Hitchcock intended - let me make the highly informed guess and let her take forever to remember that the writing was there.
Although the "showdown" doesn't hold up with the notion of these days on what is meant by spectacular it's still worked well on me - powerful stuff I would say. The humor is quite nice, I really loved the completely idiotic attempt to kill somebody by letting a flower pot fall from the window.
There are a lot of good examples of keeping up the tension in there.