And then, if the impact is large enough, you have fun effects like mountain ranges changing, seas appearing, orbits decaying/widening, new orbital bodies... you can play merry hell with your world's physical characteristics.
DM: As you exit the forest of Arek-sulit you see the mountains of Eskade.
Player: Great! It will take us about a week to get to the Pass of Uris.
(One week, game time, later)
DM: The pass appears to have collapsed due to the recent meteor impact. You now face a 900 mile long mountain range stretching a quarter of the way across the continent.
Fun sounding, isn't it?
Of course, we are talking a phenomenally huge central body to have this kind of effect, but it would be something to think about. You could even, depending on the density of the meteor, have metals formed that are different than the meteor itself, or have new, super-hard crystals form around the area of impact. Possibilities are endless. Go to Comment
The player characters, experienced and somewhat well known, hear rumors and travelers' tales about a distant area being overrun by dragons (or other terrifying monstrosities). The locals have sent them a message, begging for heroic aid.
When they investigate, they discover that nothing of the sort is going on. It turns out that a group of thieves wanted them out of the way so that they could rob them (or someone who would normally receive their protection).