I can now confirm what was in the Helvault (as you may be able to see from my previous post). It is Avacyn breaking out of the promotional material:
spindown life counters with the Avacyn Restored symbol on it, over-sized cards of Avacyn, other angels, and Griselbrand, and additionally, some Angel / Demon two sided token cards. All images of these products were spoiled a day or two before the release. I was fortunate enough to obtain the life counter and 4 of the the token cards. I did not try to get the over-sized cards - which I believe would be suited for Commander / EDH.
I am not overly impressed with this set in a sealed format, but neither am I disappointed with it. It has a feel that for this Magic: The Gathering (MTG) set, it is only somewhat connected to the rest of the block via its flavour and the undying mechanic. It did have a feel that it was made for the Commander / EDH format. I do not think this is a bad concept, but playing it in a sealed format meant I did not have much to do until turn 4 or 5. If my opponent could swarm out better smaller creatures than me, then he was able to subdue me. In my sealed pool, I did not have much that was large or any cards with the miracle mechanic - so I did not experience those mechanics. I did not feel that this set was strong enough to stand on its own. I believe that Innistrad, and even Dark Ascension were far better stand alone sets.
My final record was 1 win and 3 losses. This is a step down from the Dark Ascension pre-release where I won one more match, but better than the Innistrad pre-release where I did not win any matches.
Still, it was a great atmosphere at Games Laboratory. The staff there did a great job of organising and running the event.
Saying that, I have yet to play in a draft format with this set.
Does anyone want to comment on their experiences with the set so far?