Crimsonworld is a very entertaining casual arcade game. It has different game modes, including Quest, Survival, and Rush. In all game modes, you fight wave after wave of alien enemies. They all try to kill you by eating you, for what they have to get close to you. None of the enemies that I saw had any powers other than exploding upon contact with you, but that isn't really a problem when you move around the screen shooting them. You start with a pistol, which has quite a few rounds in it. When the rounds are shot, the pistol will be reloaded automatically. Reloading takes a second only. You are able to pick up new weapons when they appear on the screen. There are small rifles and light machine guns available. These fire faster and seem to do more damage but take longer to reload, which can become a problem.
I played the Quest mode, which takes you through several levels, in which you encounter different enemies. The first two levels were quick and easy, but after that the levels starting being longer and more difficult. I like that you get to unlock new weapons while you play. There are also other power-ups that give your bullets stopping power and replenish your health.
The controls are very easy to learn and master and the graphics are OK for a casual arcade game. The enemies aren't too smart but when they grow in numbers, they can be dangerous.