-New enemies (they appear in the latter half of the game)
-New bosses (they also appear in the latter half of the game)
-New music (most of the songs in game are covers of songs from various videogames, read credits.txt for more details).
-New graphics
-Overall an entirely new game based on the Cave Story engine.
You can download the most current version (version 0.504) here:
http://dl.dropbox.com/u/43330715/WtfStoryDemo%20v0.504.zip or
http://www.esnips.com/doc/2dec3bbe-df80-4c06-992a-b444e862a0a6/WtfStoryDemo-v0.504
WTF-story development blog - http://wtfstory.wordpress.com/
The blog updates every monday.
Also, here are some screenshots:









