Despite the fact that it's technically a bad thing, the Eclipse Cannon's laser blast was totally awesome.
Of course, the best scene with the Eclipse Cannon is when Super Shadow uses it to destroy the Black Comet.
Before doing that, Super Shadow using Chaos Control to teleport the entire comet back out into space. Now that was awesome.
Shadow gets one of these moments in Shadow the Hedgehog. His past gets revealed (Black Doom is essentially indirectly responsible for all the pain he's suffered in his past.) The way he decides to put his past behind him (and take revenge against Black Doom) is just awesome. Blasts a bloody swathe of destruction against countless aliens that got in his way, turns super, kills Black Doom in his Cosmic Horror arch demon form (complete with blowing his wings off), teleports the Black Comet onto the path of the Eclipse Cannon, and basically ensures that not a single Black Arms creature survived his wrath. Awesome.
When finishing the pure good or pure bad ending on their dark paths, Shadow stands over a battered Sonic and proclaims himself the best. Badass!
In the neutral endings, Shadow manages to take control of Eggman's entire empire, and claim the emeralds. And the only help he had all along is Omega.
Shadow's reply to Black Doom's Hannibal Lecture? "You're boring me to death, Black Doom!"
Eggman gets one in the Last Story, showing some Hidden Depths. Sonic and co. are slowly choking to death on the gas from the Black Comet while Shadow battles Devil Doom. The longer the battle goes, the more bleak it looks for them. It is at this point when Eggman finally reveals the truth to Shadow; that he is the original Ultimate Life Form, not an android he created, and confirming Shadow's survival from Sonic Adventure 2. At this point, one can imagine what Eggman's thinking that led him to state this. Respect for Shadow or Gerald? Encouraging him simply to save the world? Or has he been reflecting on his own actions, and reached some sort of epiphany?