Rocket league, h1z1, even portal 2 are great games but you'll probably need a friend or two to have more fun than playing alone :] oh and ETS2 if you like those kinds games.
Space engineers is a cool game to chill around in. H1Z1 and Raft is also two really nice and fun games. Raft is free here btw: https://raft.itch.io/raft
If you're looking to get some multiplayer games, try out Rainbox Six Siege, Town Of Salem or Rust. If you're just looking for a game to fool around with your friends, would recommend Portal 2, Keep Talking And Nobody Explodes or something as simple as Farming Simulator 15/17. You could also try out some of the singleplayer games like Undertale, or The Binding Of Isaac which are quite fun and have an amazing story, there's also a fun 2016 release called Inside, its a 2.5D puzzle sort of thing, or you could get Limbo, it's made by the same developers and also is equally fun. You can also try out Selma and the Wisp, its also a puzzle game, it has an amazing soundtrack and I actually have met the developers, and they're amazing at what they are doing.
In my opinion, one of the best games to play with friends is Payday 2. You will laugh alot and have good times
If you like cowboys and stuff like that i recommend call of juarez gunslinger.
Titanfall 2. I'm in love with the game. It's so fun!
It might be a bit over 20 pounds. I know a redeem code, it's TITAN20 but I'm not sure if it's expired or not.
The Campaign was shown to be one of the best campaigns in 2016, even though it is kind of short but it's mostly multiplayer.
Campaign trailer: