A Pleasant Surprise!
I played both previous Lego Star Wars on the GameCube and on the GBA, and I'm happy to report that the DS version has much more in common with the "real" console versions. Characters and environments are in 3D, and the levels follow roughly the same territory of blowing things up, pulling switches, using force powers and other character-specific abilities to advance. Some people have said this game resembles a 2D side-scroller, but it's actually the camera angle that is set at the most useful perspective for a 3D game on the DS. There are 5 levels per episode for a total of 30, an impressive character roster, character customization, minikits, red and gold bricks to collect, all just like the previous GameCube games. There's even some voices... battle droids say "Roger, Roger" and the little guys I'm ashamed I can't remember their name say "oo tee dee!"
In some ways this is actually better than its console counterparts, and here's why:
Minigames- I've only played a couple so far, but they are inventive and use the touch screen quite well. Speaking of the touch screen, your jedi powers are now direction-specific, so while you don't have a choice of which way the blocks will float, you are at least actually directing them as they move, instead of pressing a button and watching things move randomly.
Vehicle levels- I almost returned the original Lego Star Wars in frustration over the Pod Racer level. I couldn't tell what I was supposed to be doing or see what was coming next, and just played it repeatedly until luck allowed me to finally beat it. My 8 year old nephew had the same problem. This time the DS used both screens for a top-down vertical scrolling race that was both fast and actually fun!
So far I haven't been able to try out the multiplayer, but it's there as long as your friend also has a copy of the game. Also, I've heard that this version doesn't include in-level vehicles like the AT-ST, which is too bad.
So to summarize... a surprisingly good translation of the Lego Star Wars Saga to the DS. Graphics and sound are solid. Gameplay is solid. Replay value between story, free-play, and minigames is solid. I actually prefer this to the console versions, since most of that content is recycled and this version is both portable and completely new. I wouldn't play a Lego Star Wars game for the great graphics anyway, and the portable, more bite-sized levels are actually a better way to spend time in this game's world.
Hope this helps somebody, and enjoy!