One game that I miss playing the most is Day of Infamy. I believe it was originally a mod for Insurgency, which was a Source engine mod turned into a standalone game, and the same happened to DOI. It is basically Day of Defeat, updated in the latest version of Source engine at the time, and it was a blast to play. It had its peak player base around 2017-2018 with nearly 10k concurrent players (if I remember correctly there was a free weekend when it first launched to attract players). Ever since then it has been dwindling in players, with SteamCharts saying there is only 45 people online now.
My friends and I have made so many great memories in that game. It was the perfect mix of arcade shooting, tactical thinking, and strategizing plans to win the match. The shooting felt fantastic, movement was fluid, nice mix of weapons and gadgets. and whenever they added new maps it was a celebration.
I know New World Interactive went to focus their time in Insurgency Sandstorm which is a fantastic game in its own right, but I hope that one day they will bring back Day of Infamy in Unreal engine.