I have posted on Lego robot creations before. Well those were made with NXT 1 and 2. Now the new version is out in time for the 2013 holidays. NXT stood for "next" while EV3 stands for "evolution". And the EV3 does have several significant changes. In terms of looks, the EV3 is a little more geometric than NXT and a whole lot scarier! That Mohawk is intimidating!!! :-]
The EV3 has some new sensors. The old ultra-sonic sensor, which was known to be inaccurate (and I can testify that's true), has been replaced by an infrared sensor, which is promised to be more accurate and can also function as a remote receiver. Also there's a remote that you can program that sends signals to the infrared sensor/receiver. The color sensor hasn't changed, except for getting the updated look I described above. The number of touch sensors has been reduced to one, but I think it's a fair trade off for all the other improvements. Also one of the classic motors has been exchanged for a forward facing medium motor. There is a pretty obvious similarity between this new motor and the "power functions motor" that Lego sold with the original Technic sets. This new motor is very helpful for motorizing smaller attachments, where doing so with the bigger motors can be very awkward. The new intelligent brick has a higher resolution screen and a much better processor allowing for faster and more complex operations to be carried out. They've also changed the programming language/interface to make it even more visual!
Overall, the EV3 is pretty is pretty cool, but if you already have an NXT 2.0, I have to say don't bother. Really the only changes I find very important are the new motor, infrared sensor, and the higher power brick. And it costs $350 when you can get a used 2.0 for a lot less -- you're getting a used NXT for more than $300 you are getting ripped off by someone who wants an EV3 instead. If you have an NXT, you also might consider just buying the new motor and IR sensor. Here's a link to the official Lego Mindstorms page.