Going into May 2011, many of the games from April’s top 25 Facebook games stay with us while some foreign language games vanish. Add to that a few notable newcomers, and you’ve got our top 25 Facebook games for May 2011.

First up, we sort the top 25 by daily active users. This gives us an idea of which games people tend to visit habitually. Be sure to compare this list to the top 25 monthly active users list for an idea of which games have a higher retention rate (or “sticky factor”) with players. Remember that DAU is vulnerable to sharp fluctuations as a result of ad campaigns, technical difficulties, and holiday lulls when people aren’t visiting Facebook when they usually would.

Our first notable newcomer on this list is Playdom’s hidden object game, Gardens of Time, at number 16. The game has seen rapid growth since its early April launch, routinely making our weekly lists of top 20 games by growth. Players progress through a story-driven sequence of missions, each being a hidden object puzzle or some variation thereof.

Next up, we sort the top 25 by monthly active users. This gives us an idea of how larger a game’s total audience is, although it doesn’t pain a clear picture of how well the game retains or monetizes among its audience. A game’s MAU isn’t as vulnerable to sharp fluctuations as DAU, however, so we can see overall trends in a game’s life cycle that tell us whether it’s thriving or decaying.

Here we see our second notable newcomer from German developer Wooga, Diamond Dash, at number 21 on the list. This bubble-popping arcade game officially launched late in March and steadily climbed the growth charts throughout the month of April before landing at its present-day DAU and MAU levels.

It’ll be interesting to see if both our newcomers can keep up the pace for another 30 days to make June’s top 25 list of Facebook games. Assuming both were supported by ad campaigns, we can expect to see DAU taper as the campaigns come to an end; however, with new viral features available to games through Sponsored Stories, both games could maintain a steady stream of new players.

All results of our Top 25 articles are based on information collected from AppData, our traffic tracking service for social games and their developers.