Shoot The Wall

You start off with a gun, and shoot a wall. Real simple. You get money for shooting the wall to upgrade your gun, until you are doing crazy large numbers of damage, with bullets going everywhere. It's all quite fun. I enjoyed it. That was less than an hour of content though. Levels two to four where the same thing. Just a tiny bit of added story. Still fun, because I enjoyed it the first time. But nothing new, or exciting. I had the whole game beat in less than three hours. I got almost all the achievements just going through the story. But then the last one, I had to run in a circle for an hour. Very unfun. Why do these games always have to add an achievement like that? To pad runtime?