I've only seen Suspiria, which I suppose is okay as everyone says it's his best film. The most frequent topic of discussion seems to be the use of colour, and I'd have to agree. After watching this, I got the impression that Rowan Woods has probably seen it too (he even uses the lightbulb shot in Little Fish).
It's described as a dark fairytale, and Argento apparently wanted to use twelve year-olds in it. The fact that he didn't hasn't hurt the picture, and Jessica Harper is the perfect choice for playing a one-dimensional figure capable of grabbing attention and sympathy from the audience, but it would be interesting to see how such a film came out. Considering the ways in which he milks tension and the absolute unpleasantness of the razorwire scene, it's probably for the best though.
On the topic of fairytales, this film has been criticised for a complete lack of character development and a minimal, nonsensical plot. However, Argento aiming for a cinematic nightmare, it is a perfect representative of a film that doesn't need character-development and a complex plot (just like a fairytale). I enjoy such things in a film as much as the next person, but the skillful manipulation of the senses and the primitive psyche is as much an achievement as being able to detail the emotional breakdown of a gritty detective in LA after the war. It's all a matter of whether the film-makers have succeeded in their goals, as opposed to meeting some proscribed set of criteria. It's a horror/supernatural thriller - it's supposed to horrify/supernaturally-thrill you.
Most fail at this anyway.
So in summation - it was gruelling and pretty. His stuff is hard to find here, but I'd like to see some more of it.
What a needless, incoherent rant.