Lucasarts have some great titles, but not all the great ones are just by Lucasarts.
Here are a few of my recommendations (which are playable with the ds port):
Lucasarts:
Day of the Tentacle
Indiana Jones and the Fate of Atlantis
Indiana Jones and the Last Crusade
The Secret of Monkey Island
Monkey Island 2: LeChuck's Revenge
Sam & Max Hit the Road
Non Lucasarts:
Beneath a Steel Sky
Flight of the Amazon Queen
Simon the Sorcerer 1 and 2
Legend of Kyrandia 3, The - Malcolms Revenge (laggy)