This is one of the few Hitchcock outright genre films.
On the one hand it simplifies psychiatry to a fantastic level, whereupon the neuroses and psychoses becomes puzzles that require merely to be put together in order to be fixed (also see Marnie.) This trope may very well predate Hitchcock, but has also been used extensively in filmed ghost stories of the time, and beyond: figure out the ghost mystery and clear the haunting.
On the other hand it is one of the films where Hitch relies on surrealistic imagery to show mental/emotional states. The first instance is a sequence of doors opening that signify the 'thawing' of Ingrid Bergman's character.
The other instance is the more well known, Salvador Dali designed, surrealist phantasmagoria which was used to depict a meaningful fantasy dream sequence that reveals, in hidden code, past experiences locked in the subconscious mind of the Gregory Peck character. It's nice, clearly a Dali - almost a cartoon in fact, in addition to just a bit silly (the psychiatrists have only days to solve it, and manage to decode it in just the nick of time.)
Hitchcock's interpretation of Jungian and Freudian theories are simplified to a fantastic level to what can only amount to an alternate, science fictional*, theory of dream analysis.
Romance, suspense and mystery as per other Hitchcock classics, so you are in good hands if this is what you came looking for.
Hitch does rely a bit much on loud noises to startle the viewer.
One of the Hitchcock Classics.
*Is documentation about brontosauruses now automatically to be considered Science Fiction?
And, now that Freudian theory has been mostly invalidated - and now that most of Freud's that is still valid is know to be the work of others - are movies about Freudian psychiatry to be considered Science Fiction as well?