"It's a very interesting intersection of eveningwear and daywear, but one that you have to be her to wear," stylist Robert Verdi said.
Hal Rubenstein, editor-at-large of InStyle magazine, gushed about Nyong'o's column dress and overall look, especially for an actress who was virtually unknown until her appearance as Patsey in "12 Years a Slave."
"The color was extraordinary against her skin. There was something so regal about that dress. She didn't muck it up with tons of jewelry, and the boyish hair made it look even cooler," he said.
Early arrivals included Zooey Deschanel in a gold ballet-skirted Oscar de la Renta with a youthful, boxy cropped top and vintage Neil Lane earrings. Other stars and nominees went for older Hollywood shimmer in slinky gold, silver and Champagne.
Cate Blanchett provided a Katharine Hepburn moment in Armani with high lace at the neck and a how-low-can-you-go back, along with Chopard earrings.
Amy Poehler picked three custom gowns from Stella McCartney, including a slinky black halter look, while her co-host for the awards season opener, Tina Fey, went for a fuller, strapless red and black from Carolina Herrera as her first look.
Amy Adams wore two shades of red in a backless high-waisted halter dress with a plunging neckline to the waist by Valentino. It evoked her risque-dressing '70s character in "American Hustle."
Dunham, yanking at the top of her Zac Posen gown as she waited for her turn on the red carpet, joked about eating and the awards season as she practiced her diva poses. "I actually ate a thick patty of hamburger before I came, like a cave woman," she joked to E!
More subdued was Elisabeth Moss in an embellished Bordeaux and black, short-sleeve gown from J. Mendel, her choice from about five she considered.
Tom Ford was Hayden Panettiere's choice — a black-and-white halter with a high side slit.
"I'd wear a plastic bag if it was designed by him," she said on E!
This year's red carpet had some bold color thanks to Reese Witherspoon in bluish turquoise from the Calvin Klein Collection and a pregnant Olivia Wilde in emerald Gucci. Also pregnant, Drew Barrymore was pretty at the podium in a gown with a sheer overlay adorned with red and pink embellishments.
Helen Mirren wore a lighter shade of green, a bespoke jade tulle and chiffon gown with a draped waist and an orchid-flower design from Jenny Packham.
Diane Keaton, honoring Woody Allen during the live broadcast, took to the podium in a Ralph Lauren custom black wool tuxedo and ultra-wide men's tie. And Paula Patton, a presenter, raised an eyebrow or two in a huge ruffle along one side of her white, form-revealing gown.