For sale: Baby shoes, never worn.
In those six words, Hemingway said more to us than many modern authors say in ninety-thousand words. Now, while I don't suggest that we all start trying to write novels with that same open-endedness (although some novels written that way are brilliantly successful), but you have to acknowledge that Hemingway did something amazing with that story--that's why people still publish it as an example of brilliant fiction so many years past his death.
The words pack a punch--yes, the story is pretty manipulative, but it takes long enough to realize that it's manipulative that you're not upset about it. You don't see where he's manipulating you--that's where many attempts at strong fiction fail is when you see where the author is guiding you. It has to be more like fishing--there's a nice, shiny lure and a hook, but you can't see where that thin little filament leads until it's too late. You want your reader flopping around on the floor of the boat, gasping for air--in some situations, you may literally want to achieve that, but let's keep it at a metaphor for now.
Now, once you realize that, you'll see where you can toss in those shiny punches (too many metaphors, right?). In fact, you can throw them in anywhere in your manuscript--please don't. True, a sea of fish hooks will catch fish at first, but then you reach that point where the fish figure it out--there's a whole heck of a lot of danger in this here sea (book)--let's stay out and warn everyone else to do the same. If you throw too many punches, they'll entually be unconscious and, again, will stay away from your work and tell other people to stay away too.
You have to put in a few fish hooks, just throw a handful of punches at the reader. You start with the offensive--throw out something big in the beginning, then let them mull it over after the initial shock goes away. When it comes back up later in the story, that scar will twinge and they'll be pulled back--and then another hook, another punch, comes at them while they're looking away. You don't let them relax for too long--that way they need to keep reading.
That's punchy fiction. Fiction you don't necessarily have the capacity to follow along with--fiction that drags you behind it rather than letting you ride the wave.
One line, one word can make it punchy enough. I talked about first lines on my blog, Demon Hunting and Tenth Dimensional Physics, and the main thing is that they slap you 'round. Find any memorable first line and look at it--if it sends any wave of emotion through you, if it sticks, remember it--that's a good bit of punchy writing.
WORDS TO REMEMBER:
Absolutes like never, always, or anything else simply final
Power verbs like kill, die, torture--anything that just exudes a certain chill of power through you
Also, those punchy lines should never, ever have passive verbs or structure--it loses a lot to have a was of has in an otherwise brilliantly artistic sentence.