Well the art direction of DF's games was always wacky, colorful and not serious. Maybe what you really dislike is that from full blown games they went to small downloadable titles, which are not as complex as Psychonauts for example. About this, I can only say that I think they did the right decision to survive after their games (which were amazing) tanked at the box office. Thanks to these smaller games, they are doing quite well. I just hope they will be doing something big once in a while.
Way to put words into other people's... mouth?
People can hate both the (maybe necessary for survival, Wikipedia reading on Double Fine was quite interesting in that regard) trend in smaller, less complex games as well as the art direction. This is the RPG Codex, we can hate anything!
If you wish they'd make games of different sizes, you can hardly begrudge someone else for wanting them to make games of different art styles. After all, if the art direction is turning people off from playing games, then it might be even worth considering whether trying something different may be worthwhile (assuming it's manageable, of course).