Roger Ebert may be endangered, Entertainment Weekly on its way to extinction. Have you noticed how many no-name critics are suddenly serving up pithy opinions about movies, books, music, and video games on the Net?

Amazon.com may have been one of the first sites, in the mid-1990s, to allow its users to share their thoughts about a book, just below the venerable Publishers Weekly or Booklist write-up. Now, such sites as Blogcritics.org collect reviews written by bloggers, and Apple's iTunes Music Store allows users to share their iMixes -- lists of favorite songs on a particular theme, like ''NJ Best," a selection from Bruce Springsteen, Bon Jovi, and other musicians with roots in the Garden State.

''The cultural influencers are changing," says Brian Kalinowski, chief operating officer of Lycos, the Waltham Internet portal. ''Expert opinion in the media used to drive culture. Now, it's peer recommendations."

Already, consumers can sample a broader range of critical opinion on the Internet -- some of it relevant and thoughtful, covering products that wouldn't ordinarily be reviewed by the mainstream media, and some of it biased or one-dimensional. (''This game rocks!" ) And marketers, such as movie studios and book publishers, are trying to figure out how Internet tastemakers figure into their relationship with their customers.

This year, for instance, movie studios have chosen to forgo advance critics' screenings for more new movies than they did during the same period of last year. The supernatural thriller ''Silent Hill" wasn't shown to critics before it opened on April 21 -- some of the first reviews showed up on the website AintItCoolNews.com that morning -- and yet the movie was last weekend's best box office performer.

And publishers such as Boston's Beacon Press are noticing that some niche titles, such as a recent collection of writings about Iranian culture, can attract more critical attention online than off. Publicity director Pamela McColl says that Beacon is still trying to assemble lists of influential book blogs -- ''there are a lot of blogs out there," she says -- but that the firm already provides review copies to some critics who write solely for the Net. Not surprisingly, McColl says that online reviews seem to be more influential among younger readers.

At press events where video game companies introduce products, Greg Kasavin has started to notice more non-journalists in the audience.

''The game companies absolutely understand the power of grassroots marketing, and so they'll invite bloggers or influential fans, people who write about games on message boards," says Kasavin, the site director of GameSpot.com, an online guide to the world of video games published by CNET Networks.

Professional critics, of course, can be engaging, well-informed guides to cultural choices. But they're also forced to be generalists, covering many different genres (music critics don't often get to specialize in Nigerian juju, a flavor of Afropop) and to write about the books, albums, or games that are likely to have the broadest appeal.

Web critics such as James Wegg have the freedom to write at length about products that'd ordinarily be ignored by a print publication, and often they write from a position of true expertise. Wegg, who lives in St. Catherine's, Ontario, maintains the website JamesWeggReview.org.

''I don't spend a lot of time doing the mainstream stuff," says Wegg. ''I love to find stuff that nobody has found yet."

One recent rave from Wegg was for the documentary ''Deeper Than Y," about a group of senior citizens who attend the same water exercise class at a New York City YMCA. It didn't get much critical attention elsewhere.

But Wegg's mainstay is classical music, and as a clarinetist and former orchestra conductor, he brings impressive knowledge to his commentaries on recordings and live concerts. (Wegg also contributes to his local alternative weekly; while the pay is better than the Web, he says his reach is far greater online.)

Online reviews can be grammatically deficient, and stories of authors imploring their friends to post glowing notices on Amazon.com are common. But Eric Olsen, a founder of Blogcritics.org, says that bloggers who post a review are much more likely to respond to feedback than, say, Gene Shalit.

''We get an average of 500 to 1,000 comments from our users every day," Olsen says, ''and those comments are a continuation of the review. It's much more of a peer-to-peer relationship between our reviewers and their readers, not an expert talking to the fawning millions."

At Lycos, Kalinowski says the site is planning to expand its rating features, allowing users to pass judgment on just about anything they encounter. And Spout.com, launched earlier this year, allows film buffs to band together and share recommendations of movies worth watching.

''In our research," says Bill Holsinger-Robinson, Spout's chief operating officer, ''we found that people are fairly jaded about the traditional critical mechanism, but 52 percent said they have more success turning to family and friends."

What I'm looking forward to is better software to sort through the Internet's cluttered closet of critical opinions and find the reviews that are most relevant to me. An average rating, like those supplied by RottenTomatoes.com or MetaCritic, is nice, but I'd also like a way to filter through a dozen reviews, professional and amateur, of books I'm considering buying, and show me just the critics I trust or the users whose taste is similar to mine.

It's hard to imagine that the Internet will eliminate professional critics, any more than it eliminated professional realtors or grocery stores. But it will probably make these critics work harder to state their opinions clearly, wittily, and insightfully, and provide more context than the typical Web reviewer.

It'll challenge them to develop into a known and trusted ''brand" -- and challenge their publishers or broadcasters to make sure their opinions can be found in proximity to the online spots where people buy video games, rent DVDs, or pay for their music downloads. Because the amateurs are already there.

Scott Kirsner is a freelance writer in San Francisco who maintains a blog on entertainment and technology, cinematech.blogspot .com. He can be reached at kirsner@pobox.com.

Comparison

Top 2005 picks* from Blogcritics.org, a website that collects and organizes reviews from thousands of blogs

''Grizzly Man"
''King Kong"
''Sin City"
''House of Flying Daggers"
''War of the Worlds"
''Murderball"
''The Descent"
''A History of Violence"
''Oldboy"
''No Direction Home"

* Selections are not ranked

Newspaper and TV critic Roger Ebert's Top 10 movies of 2005

1. ''Crash"
2. ''Syriana"
3. ''Munich"
4. ''Junebug"
5. ''Brokeback Mountain"
6. ''Me and You and Everyone We Know"
7. ''Nine Lives"
8. ''King Kong"
9. ''Yes"
10. ''Millions"

Some popular Internet critic sites:

Blogcritics.org
Collection of movie, music, book, video game, and television reviews by bloggers

GameRankings.com
Users rate their favorite video games for various platforms, from Xbox 360 to Sony's PlayStation Portable

Spout.com
New online community that allows movie buffs to share recommendations

MusicEmissions.com
Indie music reviews; slogan is, ''Music For the Rest of Us"

TelevisionWithoutPity.com
Snappy recaps of favorite TV shows