Christina Aguilera was one of the most buzzed-about celebrities that attended the 2012 American Music Awards, and for more reasons than one.

While "The Voice" mentor never disappoints in the singing department, her choice of outfit for her performance on Sunday, Nov. 18, had some viewers express harsh criticism online.

Aguilera, 31, was chic when she first appeared on the red carpet with a chin-length bob haircut, and a purple and white ombre gown. The look was simple, stunning and received rave reviews. But Aguilera returned to her eclectic roots when she hit the stage in the Nokia Theater on Sunday. The Staten Island native performed a mash-up of not two, but three songs from her latest and seventh studio album, "Lotus."  

The "Beautiful" singer wore a one-piece futuristic outfit draped with metallic stars for a intergalactic-inspired theme. She had drag queens join her and dance around as she performed "Lotus," "Army Of Me" and "Let There Be Love."

Aguilera's weight gain was also discussed on Twitter by some AMA viewers:

"Carrie Underwood is what Christina Aguilera thinks she looks like right now. And no one has the heart to tell her "NAWL.""

"Christina Aguilera looks like Snooki. No wait, that's an insult to Snooki."

"Did Christina Aguilera eat one of Willy Wonka's blueberries?"

However, Aguilera was not without her Twitter defenders:

"Christina Aguilera looked gorgeous last night. I love this dress and the diva attitude she is serving!"

"Anyone who says Christina Aguilera isnt amazing can leave nearest exit to the left thanks.'

"New hairstyle and looking gorgeous! Christina Aguilera aka Legendtina Godulara!"

Last week, she came out onstage during a live episode of NBC's "The Voice" and shocked viewers by sporting a pink Afro wig accessorized with a tiara.

The singer wore the same pink Afro that was a part of her sexy Halloween costume, with an equally attention-grabbing outfit for her duet with Cee-Lo Green. Her cleavage spilled out of her print strapless dress during the live show on Tuesday, Nov. 13.

The NBC mentor accented the look with star-spangled earrings, a black fur piece around her shoulders, and a white lace fan she held as she strutted around in her crystal-embellished thigh-high boots. The "Voice" mentors performed her song "Make The World Move" from "Lotus."

Aguilera was panned by critics when she displayed an odd hairstyle with patriotic jeans for a taped appearance on "Extra!" 

Aguilera joined "The Voice" panel for a sit-down with host Mario Lopez at The Grove on Nov. 5, to promote the reality singing competition. The "Dirrty" singer stood out with a unique braided pink and bleach blonde hairstyle. Instead of sporting traditional cornrows or a simple French braid inspired by the latest fashion runway shows, "The Voice" mentor debuted a cornrow braid on one side of her head with pink ombre tips, designed like a curled up snake.

Tags: Christina Aguilera AMAs 2012 Red Carpet Fashion