[MetalMilitia]

It's a little rough around the edges but has solid gameplay. It sounds stupid but it's one of those games which you need to get good at before it's really fun.
It's kind of like Battlegrounds in that none of the weapons are especially deadly but if you master them it suddenly gets good.

But I'm not convinced you actually like shooters, GW. So you may as well just go back to playing Runescape and uninstall Steam entirely.