Boxes from Amazon.com. (AP Photo/Paul Sakuma)

It was hard to miss all the jokes on social media Wednesday about Prime Day, the one-day deals bonanza that Amazon.com held to mark its 20th anniversary.

Shoppers scoffed at the merchandise selection, with many saying the assortment reminded them of a neighborhood garage sale.  Who, they wondered, was clamoring for a big sale on knee braces and Pop-tarts?  Others griped about how quickly some items ran out, and many said that Prime Day saved them tons of money not by giving them great discounts, but by presenting items that were so lame that there was no temptation to buy them.

[Some shoppers are not impressed with Prime Day]

It might have been tempting to conclude from all that digital eye-rolling that the sale was going to be a big flop.  And yet, Amazon reported Thursday that their Prime Day sale was massive.  The e-commerce giant said it sold more that day than on any previous Black Friday, with 398 items ordered per second. More people signed up for Prime membership trials than on any single day in the program's history.

"Going into this, we weren't sure whether Prime Day would be a one-time thing or if it would become an annual event," said Greg Greeley, vice president of Amazon Prime, in a statement. "After yesterday’s results, we'll definitely be doing this again."

Amazon said it rang up sales yesterday of 56,000 "Lord of The Rings" trilogy Blu-ray sets; 51,000 Bose headphones and 14,000 iRobot Roomba vacuums. (It had sold just one Roomba the previous Wednesday.) It was also the largest sales day ever for Amazon devices, a category that includes Kindles, Echos, Fire tablets and Fire TV Sticks.

The big haul is likely a relief to Amazon, which had launched a national advertising campaign around the sale and which got a surprise challenger for shoppers' dollars when Wal-Mart decided to launch a rival event this week.

[Wal-Mart won't let Prime Day gimmick go unanswered]

And yet branding experts say that the steady drumbeat of social media criticism should not be ignored, since it probably shows that a wide swath of would-be customers didn't have a good experience during Prime Day. Adobe Digital Index, which captured and assessed millions of mentions of the company on social media Wednesday, found that 50 percent of those mentions were related to "sadness."

While Amazon's sale has wrapped, Wal-Mart's is still underway, with deals slated to last 90 days.  A Wal-Mart spokesman said that Monday through Wednesday of this week "have been among some of our biggest days ever for online orders."

Amazon chief executive Jeffrey P. Bezos owns The Washington Post.