Aaliyah had a vocal range of a soprano. With the release of her debut single "Back & Forth", Dimitri Ehrlich of Entertainment Weekly expressed that Aaliyah's "silky vocals are more agile than those of self-proclaimed queen of hip-hop soul Mary J. Blige." Aaliyah described her sound as "street but sweet", which featured her "gentle" vocals over a "hard" beat. Though Aaliyah did not write any of her own material, her lyrics were described as in-depth. Aaliyah incorporated R&B, pop and hip hop into her music. Her songs were often uptempo and melancholy, revolving around "matters of the heart". Her songs have been said to have "crisp production" and "staccato arrangements" that "extend genre boundaries" while containing "old-school" soul music. When she experimented with other genres, such as Latin pop and heavy metal, writers panned the attempt. As her albums progressed, writers felt that Aaliyah matured, calling her progress a "declaration of strength and independence". Stephen Thomas Erlewine of Allmusic described her eponymous album, Aaliyah, as "a statement of maturity and a stunning artistic leap forward" and called it one of the strongest urban soul records of its time. Aaliyah portrayed "unfamiliar sounds, styles and emotions", but managed to please critics with the contemporary sound it contained. Ernest Hardy of Rolling Stone felt that Aaliyah reflected a stronger technique, where Aaliyah gave her best vocal performance. Others felt that Aaliyah was "satisfying rather than extraordinary", stating that she added little to modern R&B.
As an artist, Aaliyah often voiced that she was inspired by a number of performers. These include Michael Jackson, Stevie Wonder, Sade, En Vogue, Nine Inch Nails, Korn, Prince, Naughty by Nature, Johnny Mathis and Janet Jackson. Aaliyah expressed that Michael Jackson's Thriller was her "favorite album" and that "nothing will ever top Thriller." Aaliyah stated that she admired Sade because "she stays true to her style no matter what... she's an amazing artist, an amazing performer. and I absolutely love her." Aaliyah expressed she had always desired to work with Janet Jackson—whom she had drawn frequent comparison to over the course of her career, stating "I admire her a great deal. She's a total performer... I'd love to do a duet with Janet Jackson." Jackson reciprocated Aaliyah's affections, commenting "I've loved her from the beginning because Aaliyah always comes out and does something different, musically." Jackson also stated Aaliyah would have enjoyed collaborating with Aaliyah.
Aaliyah focused on her public image throughout her career. Aaliyah often wore baggy clothes and sunglasses, stating that Aaliyah wanted to be herself. Aaliyah described her image as being "important… to differentiate yourself from the rest of the pack". Aaliyah often wore black clothing, starting a trend for similar fashion among women in United States and Japan. Aaliyah participated in fashion designer Tommy Hilfiger's All America Tour and was featured in Tommy Jean ads, which depicted her in boxer shorts, baggy jeans and a tube top. Hilfiger's brother, Andy, called it "a whole new look" that was "classy but sexy". When Aaliyah changed her hairstyle, Aaliyah took her mother's advice to cover her left eye, much like Veronica Lake. In 1998, Aaliyah hired a personal trainer to keep in shape, and exercised five days a week and ate diet foods. Aaliyah was praised for her "clean-cut image" and "moral values".