I heard the first few notes of 'Both Sides Now' and immediately got weepy. Definitely top 10 saddest songs ever recorded.
It seems that the movie is about a spork (seriously) with pipe cleaner hands and googly eyes joining Woody and Buzz and the rest of the gang. This interloper 'spork' brings up questions about what constitutes a toy. Pretty existential I guess but considering I was a sobbing, blubbering mess at the end of 'Toy Story 3' it seems animated movies about toys can be pretty insightful.
Take a look at t his first poster from the movie too. Woody, walking away...saying good-bye perhaps. That's not sad or terrifying at all. Nope.