While not a point and click, Psychonauts is widely considered to be a worthy successor of the golden age Lucasarts craziness. Let's have a look at the synopsys: a runaway circus boy goes to a summer camp for psychics lead by a international team of superspy. He discovers that a mad dentist is stealing everyone's brain by making them sneeze, and in order to get him he has to travel into the mind of several deranged persons. Certainly on par with the purple tentacle trying to take over the world or the deathly travel agent, if you ask me :) .

Also, while not being a point-and-click game stricto sensu, you should really have a try at Stacking. It maybe not as brilliantly written as Psychonauts, it has some pacing issue but it's a really charming adventure (with Matryoshka dolls !) from the start to the end !