Note: This is a review of the Disney English dub.

Violence / Gore:
Not a lot. There is one point in the film in which a character threatens to eat a girl's parents Spoiler: her parents are pigs at the time. There is a scene in which a girl is being chased by a monster-type creature. It's not violent per-se... things get broken and it could be scary for young audiences.

Nudity / Sexual Content:
Pretty clean. The outfit that the main character sometimes wears is a kind of spaghetti-strap piece that shows some of her back and leaves her shoulders exposed; that said, she never looks indecent.
One character (a baby) wears an outfit that does not completely cover his rear-end. Again, he's a baby, so it's not sexual in nature.
There is one sort of flashback scene where it is hard to tell if the main character is wearing clothes or not. It's underwater, you only see her from the shoulders up, and there are bubbles. Also not sexual in nature.

Potentially problematic theological themes:
Spirited Away's plot focuses on, well, spirits. They come in all shapes and sizes, and live in a world slightly connected to our own. The spirits in general are very human-like. They mostly seem to be good-hearted (though some are easily angered/agitated). A few of the spirits use magic - in example zipping a person's mouth shut so that they cannot speak.

Other potentially problematic themes:
One character smokes. Casual drinking is briefly mentioned ("sake's on the house tonight!") but it doesn't go further than that.

*
Spirited Away was my first Hayao Miyazaki movie, and it may be my favorite of his works. The art, the music, the character interaction,... all superb. Plus I found the dub work to be amazing. Honestly, I learned a lot about Japanese culture from this movie, and it is probably thanks to Spirited Away that I started watching anime in the first place. It has a depth to it that (in my opinion) makes it accessible to all ages. Chihiro goes through real struggles, and is forced to grow and mature in a short amount of time... yet the movie as a whole is very clean. I highly recommend this film to anyone who enjoys Miyazaki's works, or the fantasy/adventure genre in general.

Violence: I don't recall very much, and what was there qualified as fantasy violence. Characters are eaten or threatened to be eaten by spirits. I can only recall one instance where a character is hurt badly enough to bleed.

Sex and Nudity: None, unless you count the bare rear end of a giant baby.

Theological Themes: As the title implies, Spirited Away is about spirits. Most of them have good intentions. A character is a witch, though she is technically the main antagonist of the movie. Some of the spirits have magical abilities.

Problematic Themes: None. I don't recall any substances or swearing.

Overall: This is by far one of my favorite Ghibli movies. Chihiro has wonderful character development and the world building is fantastic. I could seriously watch a spin-off TV series about Chihiro's adventures in the bath house. I'd say I recommend this to older children and up, due to a few scenes being a little scary for the youngest. In all, I'm glad I saw this one. It's very cute and heartwarming, and, in general, it is very well made.