The thing about Don't Starve is that none of its themes or mechanics are all that original - it's not the first survival-type game by far and clearly owes a lot to Minecraft in that sense, and its visuals are sort of cribbed from Edward Gorey. But what makes it a great game is that it's very carefully engineered. Its mechanics mesh and balance, its interface is effective, the art juicy and crisp.
Don't Starve works because it provides so many recombinations of its central premise: apart from avoiding starvation, you also have to not go insane, not get eaten, not freeze or boil to death, and more. Multiple cycles - day and night, the seasons, plus the interaction of these threats, means that new scenarios keep on coming up. You're not just hungry, you're hungry and being chased by monsters. Or you're sated and have lots of spare food, but the weather is really cold and you're going crazy.
The game is also deep in the sense that there are a lot of strategies to discover. I only found out today, after seventy hours of play, that you can gain Nightmare Fuel by hammering pig's heads during full moon! (This is useful, honest.)
What I take away from this as an aspiring game developer is that execution really matters. If you have a strong central concept - like "don't starve" - and do it well, this works better than burying the core of your game under extra mechanics and fluff to cover up the fact you haven't figured out how to make the best of it. The question then is: what other cores like "don't starve" are out there, waiting to be polished into a great game?