I got annoyed by the kooky voices used for the English version, heavily accented and way over the top "way to go!" -- it selects a "good" response seemingly at random from a list, so when other apps might go "ding" for minor encouragement this goes "congratulations!". Also it ascribes to "never say anything is wrong" which means instead of "wrong" it says "check answer" which doesn't always fit (eg if you miss getting a ball in a "goal").

I did look at providing new sound files but was suprised to find they weren't just wav/mp3/whatever in a folder.

I like some of the games; I seem to recall it's highly configurable.