The omission of the "Essentials" moniker seems to have caused some confusion. There have been quite a few threads about that. Hopefully they reconsider that tactic for the next release.
As far as the upgrade the installation of the program itself was as simple if not simpler than it was with X2. IIRC there were some problems with dropped extensions with certain methods of downloads with X2 early on that required some user manipulation but it was corrected. This, AFAIK, was not the case with X3.
As always a fast internet connection and using a download manager (or a browser with a download manager such as Firefox) will make the download go smoothly. Be sure to organize and keep track of the various components as they come in and put them in their own folder then on a backup of some sort (DVD's, external HDD, etc) in case you need to reinstall. Or of course you can just purchase the box/discs to avoid that.
The real weirdness comes in when you start trying to install/activate some of the extras like Melodyne and Addictive Drums. I had a particularly difficult time getting AD registered and had to contact their support department. It required me to use IE and do some funky disabling/enabling of browser options to make the registration take. I sent all the steps I had to take to Andrew so they could have the support guys know what's up with that so Cake support should be able to help you through if you have problems. Otherwise XLN has excellent support and they had a solution for me within a day or so. With Melodyne all went as planned for me personally but I have seen some threads where some people were having issues. Most notably in regards to those who already had the full version installed but a quick search of the forum should garner multiple threads on the topic that describe the solution.
That's all I can think of.
Otherwise X3 for the most part works pretty much the same as X2 but better. Something to be prepared to learn is the new Comping mode (took me about 20 minutes to fully understand it and I had to write the new methods down but it's pretty slick). However switching over to the Sound On Sound or Overwrite editing options will allow you to edit in a more traditional manner until you get used to comping.
Cheers.