A short list of the games I played and went WTF all the time.
Every one of these masterpieces has a unique feeling and atmosphere, original ideas and a lot of work and love put into. Originally I meant to include the 'Oddworld' series, 'Dungeon Keeper' series, 'Startopia' , 'Heart of Darkness' , 'Beyond good & evil' , even 'World of Goo'... I went wtf alright, but they weren't THAT weird. Also, all the Lucas Arts adventure games were very quirky, but the weirdness was mostly based on pop-culture references etc. Btw, if I was considering MMO's one would definitely be on the list: Dekaron (aka 2Moons), a korean grindfest with wtf all over it. I should mention I have never played 'Katamari Damacy' , 'Giants: Citizen Kabuto' or 'Armed and Dangerous'.
So here it is
^^
10. Rez [2002]
09. American Mcgee's Alice [2000]
08. Earthworm Jim [1995]
07. Penny Arcade Adventures: On The Rain-Slick Precipice of Darkness [2008]
06. Chrono Cross (2000) / Legend of Mana [2000]
05. MDK [1997] / Messiah [2000] / Sacrifice [2000]
04. Psychonauts [2005]
03. Planescape: Torment [1999]
02. The Void (a.k.a. Tension) [2009]
...
and finally, the weirdest game ever:
...
01. Woodruff and the Schnibble of Azimuth [1994]
(a.k.a. The Bizarre Adventures of Woodruff and the Schnibble)