I had a chance to play some Mario 64 multiplayer in my apartment with three friends and it was great, everyone just found a seat and started playing. Nothing to set up, no cables to hook in, they didn't have to bring a TV. It's truly a LAN party whenever you want one, and I would kill someone in front of their mother for a Doom 2 port on this thing. Think of it: a 16-player Doom 2 deathmatch you can carry with you.

DVD style case for the games.
The DS also has a good amount of internal memory to allow wireless play with only one game cart, such as Mario 64. Some games require multiple game carts, but I hope companies will embrace this feature to make multiplay more accessible.
When you choose to download games from the front end menu the DS opens up and looks for signals to begin downloading the game. The interesting thing is that this also gives retailers and wireless hotspots the ability to provide game demos and tournaments on wireless networks in the stores. Interesting. Will we start to see demos downloaded from wireless networks in EBGames and Gamestops? The possibilities are intriguing.
The other nifty feature is the PictoChat program built into every DS. It's a rudimentary chat/drawing feature that lets you talk or draw with up to 16 people at a time wirelessly. The drawing is limited, and there's no color selection, but with a little practice I got good with the software and was texting people around my apartment to test the system out.
I have no real use for it, but I did have a good chuckle when I went into the kitchen and heard my DS beep. Looking down, I saw a picture of a man with a small glass in his hand from one of my friends in the other room. I brought him a shot of vodka and we both cracked up.
While it's just a novelty for us older folks, PictoChat could be another killer app for kids in Middle School or High School, being able to send wireless electronic notes in class or recess would be pretty neat, and once one person has one at the lunch table I can see it catching on rather quickly. How soon until someone looks at their DS to see a "'Do you like me? Check yes or no.' note from CuteGrrrl9 across the lunchroom?"

I wonder if it has a demo? Nintendo has a clear style for their boxes, and doesn't stray too far here
Come on, now touch me baby. Can't you see that I am not afraid?
So now it seems like we've talked about everything but the most important new aspect of the DS, the touch screen. This is going to either open the door to new gameplay ideas and mechanics, or be utterly wasted. So what's the verdict so far?
Well, it depends on the game. The amazing thing is that in Metroid it's able to emulate a mouse and keyboard amazingly well. Your left hand works the digital pad just like the WASD keys on the keyboard and on your right hand you wear this strap on the lanyard that has a small bit of hard plastic for your thumb. Your thumb rests on the touch screen and with slight movements you can mouselook.
It felt uncomfortable at first, but after a little bit of practice it became second nature, and was amazingly precise. It felt a lot like using a mouse and keyboard in fact, and is a lot more useful than even the controller from any of the other consoles. It seems like good FPS controls have finally come to something other than the PC, and it's amusing that a portable Nintendo product was the first to do it well.
You can also use the thumb stylus to control movement in Mario 64, turning the touch screen into a sort of analogue controller. Again, it takes getting used to, but it works a lot better than you'd think.

The thumbstrap/stylus apparatus. It looks goofy, but is surprisingly effective
That's just for movement though, there are loads of other ways the touch screen is used, and the mini games in Mario 64 show a lot of them. There's a fun slingshot game where you pull back on the slingshot with the stylus and let it go to shoot and falling bomb-ombs. There's a game with falling Marios where you have to quickly draw trampolines to catch them. There's a Where's Waldo like game where you have to find Mario characters in a huge mess of faces. Feel the Magic is even crazier. You haven't lived until you have use a stylus to make a man to throw up goldfish. You heard me.
From these minigames and novel uses of the touch screen, we see how it can in fact lead to new ways of interacting with the game. Feel the Magic is full of fun twitch games that force you to have a steady hand and quicker reflexes. When the two screens are used together intelligently the whole experience is refreshing.
There's even a minigame in Feel the Magic that has you blowing out candles by blowing on the touch screen (which had me amazed until I realized it was just using the sound of air moving over the microphone to know when you "blew," but the illusion is pretty convincing).