This is the quintessential hybrid base builder and assault game. It's not quite a tower defense because you have to leave the base but not quite an assault game because the enemy actually assaults you harder as you get closer to winning. I just spent the last hour and a half achieving a 40 minute time in game in survival. The game was lagging hard and the only reason I lost was because I ventured out to try and clear some scrap so the game would speed back up a bit.
Really is nothing quite like this game.