Spider-Man sealing himself off from the rest of the Avengers & alone with a Phoenix empowered Colossus & Magik, so that they can rescue the Avengers that the X-Men had taken as their prisoners, and thenmanaging to defeat them by tricking them into fighting one another to try and reclaim a third of the Phoenix force, only for them to knock each other out. Considering Spidey is usually reduced to a background character making sarcastic comments in Marvel's Crisis Crossovers despite being Marvel's flagship character, it's long overdue.
Considering events that took place shortly afterwards in Amazing Spider-Man, with Doctor Octopus stealing Peter's life & identity and procaliming himself the Superior Spider-Man, it comes off as Spider-Man getting a last hurrah in one of Marvel's top titles.
Hope combining the Iron Fist and Chaos Magic to drive off the phoenix empowered Cyclops.
Cyclops: You see that, Xavier? They're trying to assassinate us!! This is who you side with!
[Cyclops is smashed into the ground by a barrage of ice.]
Iceman: Not us, YOU! It's just you that everyone is sick of. Damn you, Summers!
Issue 10 has a lot of awesome one-liners from Cyclops as he lays a huge beatdown on the Avengers. Most notably after he KO's Ben Grimm: "How's that for Clobberin' Time?"
In the final issue, Hope Summers, with the aid of her Iron Fist training and copying the Scarlet Witch's Reality Warper powers, fulfills her destiny as Mutant Messiah and restores the X-gene.
Some of the Av X: Vs. fights were really awesome. Daredevil vs. Psylocke and Iron Man vs. Magneto just to name a couple. Emma Frost vs. Thor was awesome as well, Emma is amazing when she gives him a No-Holds-Barred Beatdown.
The fact that although he lost the actual beating-people-up portion of the fight, Cyclops essentially accomplished everything he set out to do. Emphasized in the final Uncanny X-Men tie-in; Scott is now in shackles for the crimes he committed as Dark Phoenix, and he repeatedly asks Beast, who is detaining him, if the mutant race was restored. Beast dodges the question for as long as possible, but eventually caves and tells him that they were, and Cyclops, in response, raises his cuffed hands to the sun in the shape of an X. Whether you think AvX was the greatest or worst thing ever, the one thing everyone seems to agree on about it is that his character arc, from New X-Men to this story, has been awesome.
The fact that Professor X manages to take on Phoenix! Cyclops in a psychic duel, and put him down over and over again, only losing when Cyclops takes the whole Phoenix Force for himself.