For my frontpage the change is small but still noticeable:

/r/pcm was always holding on by a thread, it looks like all the quality posters and moderation have left/given up.

/r/chess is down about 10-20% of its normal upvotes

/r/ProgrammerHumor is down about 50%

/r/Sysadmin is surprisingly normal-ish for upvotes, but the posts aren't great. Although that sub has been mostly off topic rants for a while now... not sure I want to purely attribute that to the API change.