I suppose it's common with these updates to have miscellaneous things broken that were fine before (along with a settling-in period that is likely to cause battery drain for awhile). I haven't seen too many of the problems reported here. I just tried Gallery, for instance, and it actually seems noticeably faster than before.
The one complaint I do have is the one several others here have noted: I use folders on my Home screen to hold quick calls and contacts, and when I tap one and go to Phone or Messaging, then back to Home screen, the folder is still open (and, I think, looks uglier than it used to). I upgraded to the S4 last summer from an earlier Samsung phone running Android 2. In that old OS, this was the standard behavior with Home screen folders, and I was delighted to find that it was no longer so in Android 4.2. And then, having fixed it, they apparently deliberately broke it again! Why, why, why on earth? Yeah, I know, a whole extra second out of my life. But still--why?
As for World clock, it doesn't crash for me--but it did apparently reset to 3 random cities besides my home town, and lose the ones I'd put in before.