The link above shows all the upgrades from Ice Cream Sandwich, which is much more than what I could have pointed out. A lot of it definitely sounds good, and the one that sticks out the most is how Google is available from the lock screen. In fact, using Google on the phone is even easier with a whole new Google interface than on 4.0 which is pretty cool.
Upon unlocking straight to the new Google interface, it displays some "cards" with relevant information to you. Using GPS locations, it can tell you the weather in your area, what restaurants are open near you, show you what the traffic is like while traveling, etc.
Another important thing to mention is that it has greatly improved my connectivity to 3G and 4G compared to how spotty it was on Ice Cream Sandwich. Perhaps it was some weird coding or behavior bugs, but after switching to Jelly Bean, I don't think I really lost connection at all when I went out earlier today. If my phone's connectivity stays this way, then that's one major issue fixed from my original review for the Galaxy Nexus, leaving only the battery life issue. (After checking my phone for the past several days, at many different places where I don't have Wi-Fi so phone signal is even more important, it retained its signal whenever the signal was there. There was an area with weak signal where I actually lost signal while I was there, but otherwise, I did not lose signal for 10+ seconds randomly like it did before on Ice Cream Sandwich.)
Considering how great the pros are in this upgrade than the cons, the Jelly Bean upgrade is a must for the Galaxy Nexus IMO. Now, maybe I should look into the expanded battery for this phone to reduce its flaws some more...
Edit: The battery problem can be mitigated by opening the App History screen, and swiping everything you don't need off to clear them. The phone's processors were being used to keep those apps running in the background, which was eating up more power even when you weren't using them. By doing this, it can easily save you several extra battery hours.