You would think that making a game free would be enough to get people to continue playing it, but that's not the case. Happy Wars has continued to be successful because it keeps providing new content and updates. If these don't tickle your fancy, how about a weekend of Double XP?
This weekend heralds Score-Galore. You will get double experience points when playing any campaign, co-op or multiplayer mode. The XP can be exchanged for better weapons and stats for your characters, or just a natty new hat. You have until Monday the 15th July to make the most of the offer in this 15 player co-op game for xbla.
Co-Optimus gave Happy Wars a solid 3.5 and, since this, the game has been developed further. It is free-to-play, so is worth checking out just to see what it is like. You never know you may just find yourself enjoying warfare.