The main difference that I have noticed is battery life. It seems to last me almost 3 days on a single charge with moderate usage. I used to only get about a day and a half, so almost double which is amazing for a smart phone. Poor iPhone users I know can manage a day at most it seems even with moderate usage. Now I'm not a power user, and have my phone idle for most of the day while I'm at work, but still, 3 days is pretty good.
The other thing, which is the biggest thing for me is the increase in Apps for the store. A lot of the apps that I was reading about, or hearing about weren't on my old phone because of the older version. Now I have updated apps with features that take full advantage of my phone.
The one downside, that I had to go through is that it wiped my phone clean of any data I had on it, such as previous apps, so I haven't gotten all of my old ones back, but have gotten most. This was a bummer because I had some cool ones that I have forgotten the names of, so I need to try to remember, or will remember when I have a use for them.
Overall, I think this was a good update and recommend anyone that can should get it done ASAP.