Nintendo's done it again.

The new Nintendo DSi handheld gaming console, which arrived in stores April 5 for $170, is a quantum leap forward from the similar-looking DS Lite. It adds another layer of applications and functions to the core DS system to become the first Nintendo handheld that's plenty of fun even without the games.

My pig-tailed game-testing assistant, age 7, had nothing but praise: "It's very great. Almost all of my friends want it."

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But back in October, when the Japanese video-game titan made the surprise announcement that it'd be introducing yet a third edition of its wildly popular DS, the news didn't appear to make sense.

Nintendo had already reduced the size and weight of 2004's blocky original DS with the slimmer, prettier DS Lite in 2006, a redesign that expanded the handheld's market beyond young boys to their sisters and older siblings.

Worldwide sales of both DS models were approaching 100 million units, a threshold that's since been passed, and the addition of a third, pricier model (the DS Lite costs $130) seemed to risk market saturation.

The single new feature promised in the DSi — as in "eye," or "individualization" — sounded like a throwaway gimmick. Two low-resolution digital cameras, one in the hinge facing the player and the other on the outside shell? Big deal.

There were a couple of technical upgrades as well — more memory, more storage capacity and the addition of an SD card slot — but compared to the much higher-powered PlayStation Portable, Sony's handheld console, those seemed like a feeble attempt to catch up.

Well, I was wrong. The DSi is a huge expansion of the DS's capabilities. It adds a whole new layer of functionality to the DS interface.

Now playing game cartridges is just one application among many — one that can finally "hot-swap" cartridges in and out without having to turn the unit off.

The previously existing Pictochat and Download Play functions are applications as well, but it's two of the new apps — called just "Camera" and "Sound" — that really sell the DSi.

"Camera" not only takes pictures, but lets you manipulate them with different lenses, distortion effects, overlays and filters. You can stretch and swirl images with the touch stylus or your finger even before the shutter's clicked, or use various mirror effects to create kaleidoscopic images.

"I can't believe that you can take a picture and then color it in and then make a frame," said my lab assistant, who shall remain unnamed to protect her privacy. "I like making my pictures wacky and to spread my face on the DSi."

The Camera software automatically recognizes faces, so you can add preset templates of mustaches, glasses, funny ears and noses to your own images, or even merge two faces for truly weird-looking portraits.

The effects work on both new and archived pictures, which can be saved either to the DSi's 256 MB of onboard storage or your own SD card.

I whipped out the DSi in a room full of second-graders three days before the model went on sale; the boys instantly went nuts, and the girls had a blast playing with pictures.

The "Sound" application lets you record brief clips, up to 10 seconds, of your voice or an instrument, and then manipulate them in different ways.

There's a pitch/speed shifter, an effects filter with presets including "electric fan," "tunnel," "robot" and ''8-bit game" and a toggle to play sounds backwards and forwards.

Using an SD card, you can play AAC-format song files (sorry, no MP3) and use the same effects on those as well, though you can't save the manipulated versions.

A series of play-along sounds lets you clap, drum or scratch to the beat using the left and right triggers; this being Nintendo, there's even an entry for the "Super Mario" jump and coin-grab sounds.

Your prerecorded clips can be overlaid on the songs, and there's also a goofy visualizer that shows sound waves not only in oscilloscope and equalizer formats, but as dirt-bike hills, ski slopes, Super Mario coins (which of course you can grab), ripples on a pond and my favorite, an "Asteroids"-type vector-graphic spaceship shooting missiles through a space tunnel. My lab assistant's 4-year-old brother had a lot of fun with that one.

The third pre-installed new application is the Nintendo DSi shop, a welcome addition to the DS lineup that lets you download games. Like the Wii Shop, you pay for games by using "points" purchased online with a credit card or with a point card from a store.

I got 1,000 free points simply by signing up for the shop, a practice Nintendo says will continue until March 2010; games and other applications cost between 200 and 800 points.

After several misfires due to a continually dropping Wi-Fi signal, I was able to download Nintendo's modified Opera Web browser (for zero points, a nice change from the $30 it had cost for the regular DS and DS Lite) and the game "Wario Ware Slapped!" (500 points) by laying the DSi right on top of my wireless router.

(I'm not sure if the balky Wi-Fi has to do with my ancient router or the unit itself; PCs, a TiVo and even a Wii have had no connection problems, but a G1 phone barely gets a signal.)

The Opera browser works fairly well. Pages load briskly, with the entire page showing on one screen and a highlighted section on the other, and it's easy to switch each between the touchscreen and the display screen for easier browsing.

Oddly, some "mobile" versions of popular Web sites defaulted straight to the regular sites. And again, the Wi-Fi connection kept getting dropped, which resulted in my giving up the Web-browsing endeavor quickly.

As for "Wario Ware Slapped!", is a great idea that's poorly executed. Players make gestures and faces that are seen by the DSi's camera in order to play a series of minigames set in an amusement park — think the Wii game "Wario Ware: Smooth Moves," only without the Wii controller.

The problem is that the software can barely see you. It needs bright light and high contrast to make out your eyes, mouth, hands and the shape of your head.

It couldn't tell the difference between my olive skin and the yellow wall behind me, or make out my eyes very well — strange, considering the regular Camera software got it all right away.

I can only imagine "Wario Ware Slapped!" must have been calibrated by light-skinned, black-haired Japanese technicians in well-lit labs. I hate to think what'll happen when darker-complexioned people try to play.

Physically, the DSi does lose one feature found on the original DS and DS Lite: the second cartridge slot that let the older models play Game Boy Advance games.

What this really means is that Nintendo has finally moved on from the GBA platform — the last original game for it was released in 2006, and it's now listed as a legacy system on the company Web site.

Unfortunately, it also means that the two "Guitar Hero On Tour" games, which plugged a 4-button "fretboard" into the GBA slot, can't be played on the DSi at all. Nor can the optional DS "Rumble Pak," which gives some tactile shake to games, be used.

Otherwise, the DSi's case is a barely perceptible modification of the DS's. The body is a tad bit longer and thinner; the screens are a little larger; some of the buttons have been moved.

The most noticeable difference is that while the DS's glossy body picked up smudges and fingerprints easily, the matte-black (or matte-blue) DSi is smooth yet smudge-free.

So is it worth spending $170 to upgrade from the "fat" DS or DS Lite? Probably not. Gameplay is exactly the same.

If you don't already have a DS, would it be worth paying an extra $40 above the DS Lite, which will presumably still be manufactured?

Yes. The camera software, sound software, SD card slot and downloadable content give it new dimensions of enjoyability the DS Lite will never reach.

"It's better than all the video games I've ever played," said my lab assistant. "[With the Wii,] you have the Wii controller — but you don't get to write on the screen."