Don't get excited...
If you have the ability to play TR:Legend on ANY other platform besides DS do yourself a favour and play it on that. The DS doesn't suck, but it is certainly the worst port of all. The PSP version is better if you want to try it on a handheld unit.
The touch screen is used to shoot enemies but it is really badly done. You touch the little men on the screen with the pen, they die. That's it. And the enemy AI is so useless you can wipe out everyone on the screen before they even get a chance to hurt Lara.
Graphically it is OK, but Lara looks like cardboard, in fact it all feels a little 2D, which is not that bad in itself, however it does become a problem when you have to judge depth for jumps and so on. You will plummet to your depth a number of times throughout the game because you misjudged the distance.
Fun, but could have been better.