I like the idea of a crashed spaceship...sometimes fictional worlds are much more fun to look at after they have been ruined. They become mysterious. To maximise awesomeness make sure the spaceship crashes in a rainforest, and atleast one giant spider colony setups in the wreckage. Also malfunctioning robots roam the general area. Other stuff could be brought in later, like a bunker full of shut down robots, which were to be turned on after landing but things didn't turn out that way...or buried terraforming devices, the occasional genetical experiment gone wrong (GIANT SPYDARS). To add more mystery you could say the ship had been shot down, which is one of the reasons no rescue boats apear, because the aliens have destroyed all the other human worlds (although they didn't know there are survivors on this planet
, it will be their greatest mistake!!)
On the other hand, you could dump the sci-fi thing and do a fantasy caveman thing, with giant dinosaurs and general prehistoric stuff. Everybody likes dinosaurs!