Well, not sure what console/systems your brother has, but if he's a fan of COD, he might enjoy games like "Rainbow 6 Siege" (I'm a big fan of this one) or "Rainbow 6 the Division". The Division had a rocky start, but it's gotten a lot better due to updates since it was first released. Although I don't really care for it, I know that "PlayerUnknown's Battlegrounds" just got its official release today (?), and it's had an extremely popular beta on Twitch for the past year or so.
Aside from those, there aren't really that many shooters that I follow, so sorry that I can't be of much more help.