While typical Marvel summer events have been daunting in their scale, the first issue of Original Sin is starting small. While these big summer event books tend to be loaded with huge battles, this could conceivably be very effectively executed if Jason Aaron instead opts to stick with a detective angle for this story.
At the onset of this first issue, Uatu, the Watcher, is violently murdered by an unseen assassin, unseen to readers that is, but not to Uatu.
This murder is the set up for the remainder of Original Sin that will unfold over the next few months and (unfortunately) across many titles in the Marvel Universe.
The cast thus far is probably the most interesting part. Following Uatu's murder, the standard Avengers are on the scene, but they bring along with them the retired Nick Fury. Having not been part of a Marvel event in a few years, it's nice to have Nick back on the scene. After visiting the moon to examine the scene of the crime, Fury and the Avengers call in specialist heroes from around the Marvel U to embark on a fact-finding mission and begin the legwork on the case of the Watcher's murder.
It isn't explained why these particular characters were chosen for their respective missions, but the rosters are interesting, and will hopefully make for something a bit different than most other Avengers-centric Marvel events. The cast thus far includes Black Panther, Ant-Man (Scott Lang, gotta hype those Marvel movies), Emma Frost, Dr. Strange, The Punisher, Winter Soldier, Moon Knight and Gamora. Now, if that isn't a motley crew, I don't know what is.
At the end of the issue we are left with Spider-Man and The Thing battling a Mindless One in New York City. What makes this Mindless One different though is that it has not only developed a telepathic power set, but it uses the Ultimate Nullifer to commit suicide. On the final page of this over-sized first issue, we discover that the crime of Uatu's murder was committed by more than one person, and the reason for the crime seems to involve the now-deceased Watcher's eyes.
An interesting start to this event, and I hope that Aaron steers clear of the big shoot-em-up, intergalactic battles that have become commonplace in the 616 over the last decades worth of event cycles. If this ends up being a "who dun it" type detective/adventure story, I will be more than happy to see this one through to completion.