Alternative Character Interpretation: Loki. In the main story, he realises that his actions have gone too far when the Void is let loose and was destroying Asgard. However, the Siege one-shot focusing on him reveals that Loki had a greater agenda which would be expanded upon in Journey into Mystery (Gillen). Was Loki's Heel–Face Turn and Redemption Equals Death a genuine attempt at atonement, or was it simply part of the plan?
Badass Decay: Asgardians, who have previously been described as one of the most powerful armies in the universe, fall like flies in front of Norman Osborn's army, including those who are only humans with normal weaponry. Justified In-Universe: In Thor #11, Balder states that, as long as the Asgardians are on Midgard (Earth), they are more vulnerable than usual and can be killed more easily.
Catharsis Factor: After how much he made life hell for the real heroes of the Marvel Universe, seeing Norman Osborn finally be exposed to the world for the depraved lunatic he truly is and imprisoned (along with most of his cronies) can be quite the satisfying experience.
Nightmare Fuel: Everything about the Void, from the Gorn of a changed Sentry ripping apart Ares to the reveal of its true demonic appearance to Sentry's charred corpse after Thor is forced to Mercy Kill him.
There's also the extremely unsettling reveal of its nature as the Angel of Death. Osborn pronounces that the Void simply is Death. Its the end of all things. You'll meet him when you die, sooneror later.
Signature Scene: Sentry ripping Ares in half is easily the most memorable part of the storyline.
Tear Jerker: Thor's reaction to Loki's death. For all his villainy, Thor still loved him.
Norman was taking on the entire Marvel Universe, but he's still primarily Spider-Man's main villain. As such, it would have been nice if the webslinger had been more involved in taking Osborn down, as all Spidey did was get the last punch in after it didn't matter anymore.