The OMFG moments in FS2 for me were:
* Colossus arrives and reduces the NTF corvette to wreckage in one shot (why do you always find yourself in the best observer position the FIRST time you play the game? However hard I try, I can't recreate the moment when three HUGE Beams come out of nowhere and vaporise that Corvette)
* Sathanas arrives, I go to investigate the massive warp effect, and get vaporised by an enormous Beam cannon which comes out of nowhere.
The 'OH CRAP!' moments were:
* A bunch of NTF Myrmidons turning on me ('...but hate the traitor'), although that was more like 'bring it on, *****es!'
* 'DIVE, DIVE, DIVE!' Push stick forwards, engage max AB, look back and see the Sathanas miss me by miles. I then think, 'well, that wasn't too difficult.'
The supernova was a case of, 'hmmm, I'm right next to the node...'
I suppose I'm just naturally lucky.