I've been looking for good multiplayer games for a while, my favorites are
-Minecraft
-Terraria
League of Legends
-Age of Empires 2
-Warcraft 3 TFT
But does not have to fit, just mentioned what I still play / like, search through Steam regularly, but find nothing suitable
If you are looking for an adrenaline-charged game I can recommend you Escape from Tarkov
One of the best hardcore survival first person shooter I know
You have to buy on the homepage.
The game is pretty challenging. Especially alone
How about Insurgency? Alternatively, Insurgency: Sandstorm, hardcore multiplayer shooter, where teamwork and realism are the main focus. You can tip over there with just one shot.
Or how about 08/15 team tactics in CS: GO? Maybe also Rainbow Six: victories? If you're more interested in strategy then you should get Civilization or the old C & C parts on cncnet.org
Three free online games that could be interesting are Paladins, Trove and Dauntless.
Other online games I also recommend are Monster Hunter and Overwatch.