Companies have failed for many years to produce a successful electronic reader, a dedicated device that would do for books what Apple’s iPod has done for music — allow you to carry around large numbers of titles and enjoy them in a convenient way.

Just a year ago, Sony took another stab at this concept with a product called the Sony Reader. Like the iPod, it was linked to an online store where you could buy thousands of titles that could be downloaded to the Reader. Unlike the iPod, it hasn’t been a hit with consumers, partly because the store was hard to use and had a very limited selection.

Now, the biggest name in online book sales, Amazon.com, is entering the fray with a $400 electronic book reader called Kindle that aims to succeed by offering a much better shopping experience.

The Kindle is the first e-book reader that allows you to select, buy and download titles directly to the device, instead of downloading them to a PC first and then transferring them over. Amazon is offering a large collection of digitized books — about 90,000 — compared with fewer than 25,000 for Sony. The Kindle also can download newspapers, magazines and blogs directly, and update them automatically. This is possible because the Kindle comes with free, built-in wireless Internet access, using a cellular data network.

I’ve been testing the Kindle for about a week, and I love the shopping and downloading experience. But the Kindle device itself is just mediocre. While it has good readability, battery life and storage capacity, both its hardware design and its software user interface are marred by annoying flaws. It is bigger and clunkier to use than the Sony Reader, whose second version has just come out at $300.

Like the Sony, the Amazon reader uses a high-contrast, but low-power, screen technology. The Kindle’s six-inch screen can display only monochrome text and gray images, and there’s lag time and a flash of black every time you turn a page. But I did find that the screen was good enough to make me forget I wasn’t reading the book on paper.

The Kindle holds about 200 titles in its internal memory, and can accept memory cards for storing more books, periodicals and blogs. You can also keep and read some types of personal files and photos on the Kindle, but you have to email them to Amazon for conversion to a proprietary Kindle format.

The battery lasted me a couple of days between charges with the wireless on, longer if I switched it off.

Using the well-organized Kindle store, I was able to purchase books like “Boom!” by Tom Brokaw, “Stone Cold” by David Baldacci and “American Creation” by Joseph Ellis. The process was fast and simple, partly because the Kindle comes preconfigured with your existing Amazon account information.

New releases and bestsellers cost $9.99 each, compared with a typical Amazon price of $15 to $20 for the paper volumes. Prices for other books vary widely, but are generally cheaper than the paper versions.

I also successfully subscribed to electronic editions of The Wall Street Journal, the New York Times, Time magazine, and several blogs and news feeds. This was a much less satisfying experience. The layout of these publications was much clumsier and harder to use than on the Web, and they cost more. Blogs and periodicals that are free on the Web cost anywhere from 99 cents to $14 a month.

The Kindle has some nice software features. It includes a small keyboard that lets you make notes in the margins of books and perform searches. There’s also a built-in dictionary.

But the device is poorly designed. It has huge buttons on both edges for turning pages forward or backward. They are way too easy to press accidentally, so my reading was constantly being interrupted by unwanted page turns. Plus, the buttons are confusing. One called “Back” doesn’t actually move to the previous page, but supposedly to the prior function. I never could predict what it would do.

The “Home” button for returning to the list of content on your Kindle is tiny and located at the very bottom of the keyboard. There is no button to take you to the online store; you have to open a menu and scroll. The book-like cover, intended to protect the device, attaches so weakly that it’s always falling off. And because the power buttons are hidden on the back, reaching around to use them practically guarantees you’ll knock off the cover.

The software interface also is clumsy. There is no way to organize titles into groups or categories, so you have to keep turning pages in the Home area to find a particular item to read. And doing many tasks requires you to scroll a barely visible silver cursor along a narrow side panel.

Also, there is no way to email friends to tell them about books or articles, send excerpts or links, or even buy them a Kindle title as a gift.

Amazon has nailed the electronic-book shopping experience. But it has a lot to learn about designing electronic devices.

Email me at mossberg@wsj.com. Find all my columns and videos online free at the new All Things Digital Web site, http://walt.allthingsd.com.

Corrections & Amplifications

The Amazon Kindle is the first electronic book reader that allows users to download books via wireless broadband, without a PC. This column erroneously said it was the first to allow such direct book downloading via any means. Some early attempts at electronic book readers had built-in wired phone modems for downloading books.

But this month, Sony is taking a new whack at the problem with a sleek, attractive $350 device called the Sony Reader. The Reader tries to take advantage of two developments since 1998: cutting-edge technology for improving screens and battery life, and the example of Apple Computer’s iPod and iTunes, which showed how a great gadget with strong software and abundant titles can create an end-to-end digital content solution that consumers will embrace.

The Reader can hold about 75 books at one time in its internal memory and can accept add-on memory cards to expand its capacity. In addition to books, the Reader can also store and display Microsoft Word documents, text files and Adobe PDF files, so you can take personal or work documents with you. It even works with music files and photos.

I’ve been testing a Sony Reader for about a week and have been evaluating not just the hardware itself, but the whole system. That includes the PC software that downloads and organizes the material and transfers it to the reader; and Sony’s new online electronic bookstore, where you can buy books for the reader.

My verdict is mixed. The Reader is a handsome device with a stunning black-and-white screen and terrific battery life. But it has some serious limitations. The software, called the Connect Reader, is simple and plain, but effective. The online bookstore, called the Connect eBook store, has only a modest selection compared with a physical bookstore and is hard to use.

The Reader itself is small, slim and light — about the length and width of a large paperback book, just a half-inch thick and about nine ounces in weight. It’s cloaked in a flexible black cover that folds back to reveal the screen and a handful of easy-to-use buttons.

The key feature of the Reader is its high-contrast, but low-power, six-inch screen, which is quite different from the screens on laptops. Unlike those power-hungry displays, the Reader uses a new technology called Electronic Paper from a Massachusetts company called E Ink. This screen needs no backlighting and consumes no power until you change what’s being displayed by electronically “turning a page.”

The contrast between the black text and the light-gray background isn’t as good as on a paper book, but it’s easy on the eyes and makes the Reader usable even in bright sunlight.

You can select from three text sizes for books and switch the screen between vertical or horizontal orientations.

Because it uses so little power, the Reader has strong battery life. Sony says the Reader can perform 7,500 “page turns” on a single battery charge. Most people could go days, even weeks, without having to recharge, unless they play a lot of music or view a lot of photos.

The Reader’s screen can’t display color and is only fair at graphics because it has just four levels of gray. So photos appear in gray, and titles that make heavy use of charts and graphics don’t display well. Also, it’s too easy to accidentally press buttons and land far from the page you were reading.

The electronic books cost less than print or audio versions. I bought Bob Woodward’s “State of Denial” from Sony for $13.59. Amazon.com charges $17 for the print and audio editions. In at least one of the books, George Orwell’s “1984,” which comes free on every Reader, I found typos that were inexcusable.

In my tests, Word documents looked OK, if not perfectly faithful to their layouts. But the Reader’s claim to display PDF documents proved hollow. In every PDF document I tried, the text was nearly unreadable and the text resizing feature of the Reader didn’t help. Sony concedes that PDF documents work well on the Reader only if they are created for the Reader’s screen size and resolution. But it includes no conversion software to make them fit.

Another big disappointment: The Reader lacks a bunch of features that would enhance the reading experience. You can’t enter notes, search inside books or documents, or look up words in a built-in dictionary. And while you can bookmark pages for later retrieval, you can’t highlight passages. Sony says it’s working on a future version of the Reader that can perform these tasks.

The Reader software was fine at organizing and transferring books, and at importing your own documents, music and photos to your PC, then transferring them to the device. But it doesn’t automatically synchronize material. The online bookstore is poorly organized and has an awful search function. Its 10,000 titles are only about 10% of what you’d find in a typical big bookstore.

Overall, I’d call the Sony Reader a good start — impressive in some ways, but clearly a work in progress. I enjoyed using it, but would advise all but hard-core ebook fans to wait for an improved version.

• Email me at mossberg@wsj.com.