This is a very short but enjoyable game.
The first part is mostly an introduction to the characters. You talk to your brother via a choice-menu, which gives the author the chance to put a lot of the brother-sister dynamics into the conversations. Downside is the almost mechanical ticking off of options.
In this part you can also experiment to your hearts content with the powersuit you found. Very much fun!
The second part switches quite abruptly to a big boss-fight. Use the skills you've learned to subdue the monster.
That's it. Short, easy, fun. That's all you need sometimes.