By this point, it almost goes without saying that Zynga is kind of a big deal. The company is valued at between $15 billion and $20 billion and it has filed the required paperwork to hold an IPO where it hopes to raise $1 billion — the IPO now has a 75 percent chance of taking place due to market volatility.

What you might not know is that users of Raptr, a social network for gamers, have spent more hours playing Zynga’s “Ville” series of games (“FarmVille,” “CityVille,” etc) than they have the “Assassin’s Creed,” “Grand Theft Auto,” “Gears Of War” and “Mass Effect” franchises combined. This fact, along with many others, is revealed in the newly published Zynga Raptr Report.

When it comes to comparing the top gaming franchises based on the share of time spent playing them, Zynga’s “Ville” games (13 percent) fall behind “Call of Duty,” “Warcraft” and “Halo.”

“Ville” games are frequented a higher number of times per day by gamers than “Call of Duty” or “Warcraft” games, but the average session length and the average time “Ville” games are played on a day-to-day basis fall well behind those other gaming franchises. This makes perfect sense to me, as Zynga players often dip in and out of games to use up their energy when tending to their farms, for instance, and then returning later in the day when their energy has been replenished.

“Ville” games have a strong conversion rate when it comes to retaining players from the previous hottest game in the franchise. The conversion rate for “CityVille” was comparable to that of “Halo: Reach” and “Dragon Age 2” and was far ahead of “Assassin’s Creed: Brotherhood” and “Madden 11.”

These stats indicate just how far Zynga has come in the gaming industry. However, the company’s success is really underlined when it is compared to other makers of social games. Since 2008, Zynga’s biggest games have 3 times the percentage of gameplay share that the rest of the top 10 social games have combined.

The vast majority of Raptr users who have tried out one Zynga game have played another title in Zynga’s portfolio. Over 90 percent of those who have played “FrontierVille,” “Treasure Isle,” “CityVille” and “Empires & Allies” have tried out another Zynga game.

The report emphasizes Zynga’s crossover potential too. Almost 20 percent of those who play “World of Warcraft” and around 16 percent of “StarCraft 2” players have tried out “CityVille.” Meanwhile, Zynga games are becoming increasingly popular among Xbox 360 players.

The report, which uses data compiled from Raptr’s launch to August 2011, also indicates the extent of Zynga’s core user base, which monetizes the games. The top 2 percent of gamers consistently play Zynga games 3 times longer than average Zynga players — 120 minutes compared with 40 minutes. Since Zynga purposely limits the amount of time players can spend on each game, those who want to play more often have to purchase in-game items (such as energy) and/or encourage their friends to play too.