Space shooters can either scroll horizontally (such as Gallaga) or vertically (such as Space Invaders). These are another variety of game that can be both very easy to make and can be big sellers (due to their popularity).

For a Gallaga, style game, you'll want to use the Side Shooter template. The speed does scroll by super slow with the template, and you have to go all the way to the right side of the screen to advance the game faster (possibly resulting in crashing into obstacles). So, you'll want to bring your right barrier in about a third of the playing field before replacing your graphics to make the game more fun (as shown in the following screenshot). Also, consider speeding up the base-movement of the game by adjusting the Forced Movement parameters of the world(s).

For a Space Invaders style game, the preset template we use will be Dogfight. It's a super slow game by default. So to make things more interesting, you may want the game to gradually increase speed (by again adjusting the Forced Movement parameters for our world). The Force Increase parameter increases your movement speed over time (from minimum to maximum). It's a touchy setting, so we've found that 0.05 is just about perfect for this type of game. Then, it's just a matter of setting the Force Max setting ridiculously high (so that no human could possibly keep up, or else the game will get boring). We set it to 400. This is how we set it up:

Finally, on the Bullet object, you'll probably want to set the Velocity much higher than the stock preset to keep up with the movement increase (as well as increase the Spawn Rate).