Agar.io is the eldest son of viral flash games (the .io game genre), and I suppose "viral" is an appropriate term given the cell theme the game is going for. It's satisfying to amass size and see your name "weedblazer420" be at the top of the leaderboard, but the game is just not interesting at the beginning when you're picking up dots and can outrun everyone, and at the endgame, where you basically can't die so long as you're paying attention.