PepsiCo first announced the move in April. It was seen as a move both to fix fading sales and score points with the health-conscious: the sweetener has been linked with health risks. At the time, the senior vice president of Pepsi’s flavors unit, Seth Kaufman, said that, “Diet cola drinkers in the U.S. told us they wanted aspartame-free Diet Pepsi.”

Well, maybe they didn’t. Less than a week into the launch of the safer soda, which uses a Splenda blend, some customers are already sounding off on Pepsi’s official Facebook page, commenting (often on unrelated posts) about their dislike of the new taste. One user writes, “Aspartame free Diet Pepsi is awful… They could have made the Aspartame free stuff a separate entity rather than ruining a good thing. In my opinion.” Another says: “Got a bunch of the new diet Pepsi. Disgusting. Will have to return.”

The critics took to Twitter as well:

The new diet @pepsi is awful!!!!!!! It always taste flat and leaves a bad after taste. I'm ok with the aspartame #nasty

— CoHeir🕊🤍⚖️ (@deeofNYC) August 19, 2015

Diet Pepsi without aspartame is so nasty #wewantaspartame #pepsi @pepsi

— shelbert (@shelby_row) August 19, 2015

I want my aspartame-laden Caffeine Free Diet @Pepsi back! The Splenda version leaves a horrible aftertaste.

— Electric Emily (@mlirhar) August 17, 2015

Business Insider ran the bold headline, “People hate the new Diet Pepsi.” (A Pepsi spokesperson told the website that some 75% of consumers surveyed prefer the aspartame-free version.)

But not everyone on Facebook was negative; some users are nonetheless thanking PepsiCo for its step toward a healthier product, like Sabrina Ray-Pittman: “Just heard Pepsi is removing aspartame from DP! Thanks Pepsi, for being the first to do this.” Moreover, new Diet Pepsi is only out in a few markets, and old Diet Pepsi is not entirely off of store shelves yet, a Pepsi spokesperson tells Fortune, so it may be early to call the new flavor a definite miss. Finally, financial blog The Street ran a staff taste test of the old and the new and found that, “the difference between new and old Diet Pepsi wasn’t so readily apparent.”

For those fearing they’ll never again get to enjoy the Diet Pepsi they once knew, there was good news last month. On an earnings call in July, PepsiCo CEO Indra Nooyi did a bit of 180-turn (the company had initially said it was killing off the aspartame version entirely) and said the old version won’t die entirely: “We’ll figure out how to make it available online.”

This story was updated with comment from Pepsi.