Early on, you come across a video teaching you how to impale Necromorphs with their own limbs. On the surface, it's just a tutorial, but the context is where it gets awesome. The engineer who recorded it was fatally wounded, and while he could still stand he decided to show anyone who might come by a way to survive these creatures. Engineers in the Dead Space universe are badass. Isaac even kept the recording and showed it to everyone in his group in the third game. Yeah, that advice helped bring down many, many necromorphs.
Now, with Stross spending so much time away from you, it's pretty much a given something bad's going to happen what with the Sanity Slippage. Come the mines, suddenly Stross appears on the other side of a gate with Ellie's fucking EYEBALL impaled on a screwdriver! You think something terrible has happened? Wrong! Ellie rises out of the background and smacks Stross across the back of the head with a giant pipe. Then she just points at Isaac and yells "You owe me an eye you bastard!"I think I'm in love.
Isaac gets one right from the start. Waking up in a straight-jacket, the man rescuing him turns into a Slasher Necromorph right before his eyes and gets ready to kill him. His response? Headbutt the fucker! Need I remind you that he ISN'T wearing his helmet at this point.
As well necromorphs are only inconvenienced by the removal of their heads in the game, they suffer a momentary stun for less than a second and just blindly slash in your direction.
In the very first chapter, Isaac, using only a flashlight and medical laser, makes a working plasma cutter MacGyver style. It's also worth noting that he does this in a manner of seconds, as a man is being torn apart by a necromorph five feet away from him. You can use an Old Save Bonus to trade in the makeshift plasma cutter for a manufactured one, but if you don't it continues to work perfectly for the rest of the game. So much for Isaac's career being an Informed Ability.
On the Isaac front again, shortly after reactivating the solar array Isaac must hurry back to Ellie. Of course, there's no time to run all the way back, is there? Isaac tells Ellie he's got it covered and using the escape pod, VIOLENTLY LAUNCHES HIMSELF OUT OF THE ARRAY AND THROUGH SPACE INTO THE ROOF OF THE SPRAWL, DODGING PIECES OF SPACE STATION AS HE GOES. After it's done Isaac stays crouched on the ground, as if to say 'Yeah, I just did that.' Unfortunately the trailers featured it. The sequence can be seen here with appropriate accompanying music.
The final boss, in which Isaac destroys the Titan Marker with his mind.
Isaac: FUCK YOU! AND FUCK YOUR MARKER!
Not only that, but just after winning the boss fight, the game heavily implies an Eldritch Abomination is involved in this somehow, at which point Isaac regains control of himself. While we don't know for sure what happened, the implication that Isaac - a normal human man - just took out an Eldritch Abominationwith his mind? All kinds of awesome.
The climax of Chapter 5, when Isaac finally meets Daina. The HSQ is about as high as it gets in the game, here. First, Daina reveals she's evil and captures Isaac, and then a gunship appears and gibs her and the Unitologists. Isaac struggles to keep from being blown out the window and escapes through a vent...and with absolutely NO time to recover, faces the biggest ambulatory Necromorph he's ever seen. After chasing Isaac down a hallway the gunship shows up again and both Isaac and the giant necromorph are blown out the window...hanging onto the gunship! And Isaac gets grabbed by the giant monster and is only able to save himself by blowing up one of the spilling fuel pods. That whole bit is one breathless extended Crowning Moment Of Awesome.
In Severed, Gabe's last stand.
The ending. After Isaac destroys the Marker, he sits down, alone and exhausted, ready to die after his mission is complete. The credits start rolling and sad music plays ... when suddenly, Ellie calls. She blows a hole in the roof of the Marker chamber with her ship, flies in and tells Isaac to get off his suicidal ass and move! Isaac, suddenly invigorated, pops his helmet back on and takes off with his repulsor boots, flying towards the ship where Ellie is waiting in the door with her hand outstretched, making it just in time before the place blows.