Browser games have exploded in popularity in recent years. Recently released statistics show that the number of daily players on some Facebook games were in the tens of millions of players, per day! However, not all games are equally popular and if you want to attract the largest possible number of players it pays to concentrate on the most popular genres.
Word games have enjoyed a real boost in popularity recently. Particularly popular with female players, and the older generations, word games attract large numbers of players and can be single or multi-player. Since word games, in general, tend to be relatively simple to develop and with low overheads in terms of performance they are ideally suited to the Flash platform.
Card and Casino
Texas Hold'em on Facebook regularly attracts 15 million or more player per day! From Windows Solitaire to multi-player card games, this is an evergreen genre which always attracts players. Again since there is little in the way of graphical overhead these games are ideal for Flash, and work extremely well as browser based games.
Since Tetris is one of the best selling games of all time, it should come as no surprise that puzzle games are extremely popular online and attract huge numbers of players. Again, with a few exceptions, they tend not to be processor hungry and so are well suited to the Flash platform. While the term "Puzzle game" can encompass a wide range of game styles, generally they are 2 dimensional, and relatively simple both in terms of gameplay and development.
There are countless other styles which are extremely popular in the browser, from shooters to driving games, dress-up and make-up titles for young girls, and sports simulations to name but a few, but the three genres briefly outlined above are without doubt amongst the most popular.