To figure out how well your keyword list will do, look at the countries that the majority are coming from. Ideally, you will want US/UK/Canada traffic.
The average adsense earnings you get from 1000 US/UK/Canada traffic is about $4.
- Target enough search volume to bring in at least 1000 visitors per day
- Go for a minimum of $100/month site
- Go for static informational pages for less maintenance
Make sure you check the company that makes the game. See if they put effort into updating the game or how well they promote their games. Often times, good games get neglected and that hurts the growth of the game. You will want to make a niche site for a good game that gets updated often to increase the longevity of your niche site.
A great example is Blizzard. They make great games and always make sure to update and improve their existing games. They got new games coming out(Hearthstone and Heroes of the Storm), so be sure to check them out to see if you want to make a niche site for it!