I wanted to start a collection of all the details we know about 2nd edition and then start a discussion about them. In looking at the previews and on some of the cards and dice there are two major differences I see from the first edition.
One, that there is now armor dice rather than a single armor level. I notice on the character sheets that there is a section for Armor and it shows a number of white die. So I would assume that characters still have a built-in armor rating as well as extra armor that can be worn that allows the player to roll more armor dice. This means that even weak monsters have a chance of inflicting damage on even the most heavily armored hero. I personally do not like this. I want Descent to be more like chess and that means less randomness, not more. In my games when the heroes stack all the armor on one or two heroes I simply ignore them in favor of easier kills. This forces them to spread the armor out somewhat and use smarter tactics to cover each other. It also encourages smart playing rather than relying on dumb luck (which is why I prefer less dice rather than more).
The second thing I noticed is that the Overlord no longer collects threat. Instead, he draws cards and is allowed to play them when the triggering condition is met. Again, I don't like this. I thought the threat system was great because it allowed me to build up threat over a period of time and then unload on the heroes all at once. It's far more satisfying (as well as effective) to do it this way and get a total party kill. Playing the cards as I get them gives the heroes time to run back to town for healing, preventing me from getting kills. I also enjoyed having more things to keep track of - how many cards are in my hand vs. how much threat I have vs. what are the triggering conditions for me to play each card. I hope they haven't dumbed down the Overlord position. I liked the challenge.
On the other hand streamlined rules, faster sessions, and a class-based hero system all sound great.