I seriously hope Samsung pushes a software fix for this OTA in the near future. It sounds as though there is considerable lag appearing. With a machine with as much hardware firepower as the S4 has, it's surprising that something as small as animations would cause noticeable lag.
I'm still rolling with my old school Evo 3D and even that doesn't experience lag with animations turned on and all sorts of apps loaded. I really like the S4 (my girlfriend got one this past weekend) and am basically waiting to upgrade until I see how some of the reported issues shake out and whether software updates fix any of them. I'm also waiting to see if Google announces anything about the X Phone this week before I decide which device I want to upgrade to.