I'd start this off by saying, expect a 40 hour campaign. It's a 40 hour campaign with constant and meaningful progression, but expect it otherwise.

This game combines base building, tower defense, and action combat elements into one single package. IMO, it works incredibly well.
Base building is simple. You find a spot you like, and within 2 minutes, you have 3 sets of walls, turrets, and energy resources up.
Action combat consists of using a huge plethora of weapons to defeat waves of hundreds to thousands of enemies. All the weapons feel useful in their own unique ways. Certain enemies are resistant to specific types of damage, so you have to keep your weapons varied. Once some waves come in, you're standing in front of a wall of turrets preparing to completely demolish everything, and it's just great.

The story is near nonexistent. The story is essentially "You came here to colonize", and ends with a "Congrats you did it" slide at the end. Most of the other stuff is just dialogue between the main character and her AI partner.

I absolutely love this game, but I'd recommend looking up gameplay to see if it's for you.