What features does the iphone 5 have that the iphone4s doesn't?

Is upgrading to a iPhone 5 worth it?

I made the transition from a 4 to a 5 so I had quite a few differences. I do not think that there are many differences in your case, but here is a link listing the differences:
http://www.pocket-lint.com/news/117233-iphone-5-what-different-new

I will say for myself that the 5 is much faster - as far as loading apps and just not being laggy. It also has amazing service when you get LTE. My LTE is much faster than my very fast wireless internet at home. I would personally wait until the 5s comes out this fall. That way you can get the brand new iPhone or you can just get the 5 for less money.