From a philosophical reasoning perspective, it needs some work. Your first clause states an opinion that is a fact, “I remember…”, but the second takes the material of your opinion as universal truth to comment on a objective quality: that it is now certainly comparatively worse because you remembered it being better.

Phrasing could be amended to

It used to be fun, but they keep changing for worse.

(Both clauses appeal to universal truths, both need defending)

Or

I remember it used to be fun, but now I think they keep changing it for worse.

(Both clauses frame the statements as being only your opinion).