“What else are you going to do on this Kindle?” asked Andrew Rassweiler, senior director of tear-down services at iSuppli. “Nothing. It’s a useless device unless you’re planning on putting books, a lot of books, on it.”

The Fire is trying to do much more than be an e-book reader, a function some say it does not do as well as the original Kindle. Slightly more than a third of the 4,500 reviewers of the Fire on Amazon have given it mixed to negative reviews, three stars or fewer. Of Amazon reviewers of the iPad 2, 22 percent have given three stars or fewer; for the original Kindle, that number is 11 percent. (There are a few caveats. At least some of the iPad reviewers bought not from Apple but from resellers, the real target of their ire. As for the original Kindle, after four years it has both a huge number of reviews — over 34,000 — and the advantage of being a known quantity.)

Many of the initial customers of the Fire seem to have bought it on a mixture of faith and hype. The striking thing even about some of the one-star reviewers is that they are regretful rather than angry. One review, couched as an open letter to Amazon’s chief executive, Jeff Bezos, began: “I have spent thousands on your outstanding site. I own and love the original Kindle. When asked about why I would buy a Fire when I had an iPad, I said that half of me wanted to just support your effort and that I believed Amazon just did things right.” The reviewer is now recommending that friends skip lunch to buy an iPad.

Gene Munster, an analyst with Piper Jaffray, has been tracking the opinions as more reviews are posted on Amazon. Since Nov. 18, five-star reviews have fallen slightly, to 47 percent from 50 percent, he says. One-star reviews have held relatively steady at about 13 percent.

“I would have expected things to be even worse at this point,” Mr. Munster said, adding that initial buyers were usually the most critical. Pricing will save the Fire, he predicted. At $199 versus $500 for an iPad, “Amazon has a lot of air cover to have a B-level product.”

Mr. Nielsen, the consultant, disagreed.

The 7-inch Fire does a good job displaying sites optimized for smaller mobile devices, he said, but stumbles when it tries to show pages designed for 10-inch tablets. “Like squeezing a Size 10 person into a Size 7 suit,” Mr. Nielsen wrote in his report. “Not going to look good.” As for displaying desktop sites, forget it.