OneMoreLevel.com is a free online games website and it has over 3000 flash and HTML5 games in over 14 categories.
Some of the most popular games on OneMoreLevel are Infectonator: World Edition, Bubble Shooter, Free Rider 2, Happy Wheels, Stark Raving Ted, Bloons TD 4, Pacxon, Pokemon Tower Defense, Multitask, Truck Launch Maniac, and many more.
These are the category of games that you can find on OneMorelevel: Adventure, Action, Classics, Defense, DOS, Funny, Idle, Launch, Music, Platform, Physics, Puzzle, Point & Click, RPG, Sports, Strategy, Trivia, and more.
If you are unsure which game to play then try this link, Play a random game on OneMoreLevel.
And then there is also the Archives of previous games.
Ira Willey is the founder of OneMoreLevel.com, he was also the founder of AddicitngGames.com which he sold it off.
You can also check out this link to Play Mystery Games Online (Over 248 games).