I just got back from my pre-release, the second I have ever done.

In my initial pool my rares consisted of Malignus, a foil Killing Wave, Gloom Surgeon, Rite of Ruin, Deadeye Navigator, Devastation Tide, and Avacyn, Angel of Hope herself.
I ended up playing a white blue angel/soulbond/flicker deck with a lot of bounce spells coming from blue and a lot of beefy flyers from white. The deck was slow, so I struggled with fast decks, but I was generally able to stabilize.

Match 1 (1/0)
My opponent was running a B/U deck that was reasonably fast. Our first game went for 30 minutes with me going to 3 life, then back up, then down to 2, then back up, then down to 1, then back up after I managed to create a life gaining combo with Nephalia Smuggler and Goldnight Redeemer gaining 8 life per turn. It lasted until I finally drew Avacyn, to which he instantly scooped. The next game was cut short due to time, match 1 was a victory.

Match 2 (0/2)
I had played this guy before and he was incredibly friendly, he was playing a three colour deck (W/G/B) and he had Sigarda, Host of Herons as his bomb. My first game was a blowout, as I just couldn't keep up with his tempo. And the second game I mulled to 5 and he dropped Sigarda turn 5. With no outs I scooped, we shook hands and wished each other luck.

Match 3 (2/0)
This guy was in fact the guy I played in round 2's friend, to which I had heard he also had a Sigarda, and was also playing 3 colour with Cavern of souls and the green 1 CMC enchantment that lets a land tap for any mana. The first game was awesome, it was the first time I was able to use some of my decks synergy. Soul-bonding Stern Mentor and milling myself I was eventually able to get back Avacyn with Defy Death, making her a 10/10 vigilante, flying, indestructible tank that he had no way of dealing with. Stomping his Sigarda to death was satisfying to say the least. Game two was a bit closer with Seraph of Dawn really working its ass off, eventually winning me the game with flyers and a lucky Into the Void, to bounce his two beefy creatures.

Match 4 (2/0)
This was another really friendly guy, he was playing boros (R/W) and didn't really have any bombs. His first play both games was him shocking me to the face, despite having creatures out he could have killed. Game one I managed to reanimate my Avacyn again, which prompted an instant concession. And game two I just managed to draw all my creature bouncing spells, and he just couldn't keep up with my fliers.

Rap Up
Avacyn may not be standard playable, but I didn't see a bigger bomb in the sealed event. The synergy with Stern Mentor and Defy Death was awesome as well. Seraph of Dawn was a powerhouse, helping me to stabilize after a brutal start and even a good reanimation target; really pulled its weight. Finally my favorite part of the deck (Avacyn aside) were the creature bounce cards, I had 2x Peel from Reality, 1x Into the Void (brutal card), 1x Devastating Tide, and 1x Vanishment. These bounce cards were exactly what this slow deck needed to help me reach my beefy, high CMC angels, and by allowing me to swing, most of the time for the win, was simply brilliant.
I ended up winning 6 more boosters from which I pulled an Angel Of Jubilation, Hellhound of Griselbrand, Desolate Lighthouse, another Deadeye Navigator, Druids' Repository, and a Bonfire of the Damned which I am quite excited about.

TL/DR Went 3-1 with U/W fliers, Avacyn is a bomb