There isn't as much of a leap from a 4 to a 4S, as there is from a 4S to a 5. Each year the new iPhone is better than the one it replaced, so the question is a bit strange. Of course it is better.
Single core to dual-core where its been ever since.
4S was the first iPhone with SMP. Dual core. Multi-threading. Not only was it a new generation CortexA8 to A9, but dual CortexA9. That is massive from UI response standpoint. Even if one thread busy, the other core can work. Its like Pentium4 to Core2.
Camera went from 5->8mp where its been ever since.
-(the 5 got very little camera bump, the 5S got a great low light boost though)
3G speed doubled hspa to hspa+
720p to 1080p video where its been ever since
Gained dual diversity antenna operation where its been ever since
Seeing a pattern?
The 4->4S has been the single largest jump in iPhone feature/performance.
The 5?...
LTE more bandwidth than practically useable on a mobile device,
Wooo! An extra row of icons! Woo!