I like it so far. It seems you've got an epic story in the works.
The only thing I don't like though is that the first two paragraphs seem kind of vague. I know that they're suppose to be vague, but I think that you could have given us some idea of what the character was doing while he thought those words. Maybe something like:
This is it. There's no turning back now. Everything that's happened, it all seems like it's been leading up to this. But he knows it hasn't. Nobody could have seen this coming. At least, not coming the way it did. There were signs, sure, but they were misinterpreted. The end, it all seems so...violent. He tightened his grip on the gun as he entered the nuclear reactor.