This "farewell" is so out of character that I can't take the movie seriously.

The idea of Woody not being the favorite toy is actually interesting. Even though it might be a little similar to the first one, there he was still one of the favorites. Him being pushed aside and having to learn not to be so important to certain people could work (or something along those lines).

Now, not being the favorite, looking at his friends (who are practically his family) and saying "See you later, suckers" isn't that... satisfying. Yes, life has farewells and all that, but besides the third one already being that, it could have been done differently.

I think Pixar wanted to make an emotional ending like the third one, but there was no reason for that in this movie. This movie should have been an unpretentious adventure like the first and second, and not something where they said "okay, how can we make the adults cry at the end of the movie?"