I don't know Don't Starve and have only played ONI for a short while, so the other answers are probably more helpful that mine, but at its core the game is about managing (and obtaining) limited resources. You start out inside an asteroid with a limited amount of oxygen and food and need to build a sustainable environment from there.

Silly fun also seems to be a big part of the game - one of the character stats (they're called duplicants in the game) is the reaction to stress, and apparently one of mine is an 'ugly crier' and another one a 'binge eater'. Two appear to have a crush on each other and spend the day avoiding work and exchanging heart symbols whenever I'm not watching.

As for the game itself - yes, I find it very overwhelming. There are short tutorials on how to navigate the map etc. and a lot of stats, but not an awful lot of info on strategy or what exactly is expected of you. So far it's still fun though.