Team Fortress 2
Even though the title came out in 2007 and moved on to F2P in 2011, Team Fortress 2 is still fun and interesting. Arguably, the reason for the conservation of freshness could be, simply, hats, but there’s a lot more going on under the hood. The game, while still recognizable from the title 6 years ago, has changed quite a bit, from a fixed class-based game to a more customization-based class-based game, with no 2 snipers really being the same.
You owe it to yourself to try it, you can leave your hat on.