2017 in .io games had (what I believe) the most success. 2016 may be the golden age, but 2017 spawned a lot more decent .io games, many of which are still being played to this day. Games ranging from Starve.io, to Lordz.io, to Moomoo.io and many more are featured here. 2017 saw the rise of mostly survival based .io games, many proved to be a huge success. Battle royales are also featured (Surviv.io, Foes.io). 2017 had a lot of great ideas and games, and I will go through the top 20.
Keep in mind, I did a lot of research to see what .io games were made in a specific year and so forth. If a game has not appeared on this list, it may be in the other videos.
Note: Some of this is my opinion and with reasons. If you disagree, feel free to comment.