Have they been getting worse, or have you been getting progressively older and farther away from being the target audience?
I'm not saying all animation is aimed at children, but this franchise definitely is.
Animation aimed at children is stuff like Dora the Explorer or Arthur. Animation from Dreamworks, Disney, Pixar, etc. are aimed at all ages. Unless an adult has some hangup about watching something that contains no sex, profanity, or gore, but that’s on that particular adult and not the whole adult demographic as a whole.
Not that I agree with Fbh, KFP 1 was excellent, but 2 is the best Dreamworks Animation picture period. 3 is the “weakest” of the trilogy (mainly due to the villain being less interesting characterization-wise compared to the prior two villains), but still pretty great.