So you've already got a Sony PlayStation and a Nintendo 64: Do you really need a Sega Dreamcast? The answer to that question is a resounding yes. You're obviously an avid gamer, you want the next generation of technology, and you don't need Sega's multimilliondollar marketing campaign to remind you of this.

But what if you own a PlayStation, you're happy enough with it, but you're wondering what's next: Should you hock the PlayStation and get a Dreamcast instead? It's not so simple.

The Dreamcast, due in stores next Thursday, is Sega's attempt to return to the under-the-TV primacy it lost with its ill-fated Saturn machine. Under its gray hood lies a 128-bit, 200-MHz Hitachi SH-4 processor, the most powerful processor yet in a video-game console (well, until Sony's PlayStation 2 and Nintendo's new system, code-named Dolphin, arrive next year). NEC's PowerVR DC chipset handles game graphics; the Dreamcast also packs 26 megabytes of memory (compared to four on the PlayStation and Nintendo 64), a Visual Memory Unit (a souped-up memory card that plugs into the Dreamcast controller), a one-gigabyte "GD-ROM" drive and a 56-kbps modem, giving it box-specifications superiority over any other game system out there.

It also sells for a hair under $200, considerably less than what the PlayStation and N64 cost at their debuts. And Sega -- having watched Saturn sunk by a poor selection of games -- has lined up third-party developers to produce games for its new box. Nineteen titles will be ready by next Thursday, with close to 40 due by Christmas from such key companies as Midway, Capcom and Namco.

Many of these games look truly exceptional, meeting or surpassing the onscreen appeal of arcade games. Sega's Sonic Adventure -- the return of its blue-hued mascot, Sonic the Hedgehog -- mixes in massive, 3-D worlds, six different characters and six different styles of gameplay with amazing results. Sega's NFL 2K, easily the best football game this year, delivers visuals good enough to make onlookers think they've tuned into an actual football game. Midway's Ready 2 Rumble Boxing combines arcade-style action and an outrageous cast of 20 boxers, each with a distinct fighting style and personality.

But some of the Dreamcast's more intriguing capabilities have yet to be tapped. Take the Visual Memory Unit, a controller plug-in with its own little LCD screen that lets players set up combination moves in a fighting game or concoct plays in a sports simulation without opponents seeing them on the TV. Interesting stuff, but NFL 2K is the only game to use this so far. And only Sonic Adventure exploits the Internet link Dreamcast's 56-kbps modem makes possible -- you'll be able to download new characters, but not play against other people online. (You can also use a Dreamcast as a WebTV-style Internet-access device, provided you add a keyboard.)

And then there's the competition, the PlayStation 2 and Nintendo's "Dolphin." A lot of gamers are saying they're going to wait until next year for these machines -- the PlayStation 2 has looked even more phenomenal than the Dreamcast in early demonstrations. But for folks anxious to taste the next big thing now, the PlayStation 2 and the new Nintendo system are just advertising and hype, while the Dreamcast is reality. Are there enough of these people around to put Sega back in the game? The answer will determine if it's "game over" or "welcome to the next level" for Sonic and his pals.

Dreamcast, Sega; $199. http://www.dreamcast.com