One of the best shooting games you will find online is the Gun Mayhem game series. It is an action game involving arenas, firearms and weapons. If you have enjoyed playing all its sequels, surely you would ask for more. You will find three games like Gun Mayhem at http://www.gunmayhem4.net/games-like-gun-mayhem/. First is the Fight for Glorton game where you will fight against enemies and damage them until they are ejected out from the playing arena. You can play in both single and multiplayer modes.
The second game is Superfighters which is an action game which also involves firearms and weapons and can be played in single or multiplayer modes. The last game in the list is Combat Hero Adventure which is an action adventure shooting game with seventeen cut scenes and played in about ten arenas. As you play on, you can unlock twelve more weapons.