Facebook (NASDAQ:FB) this week published its Games of the Year list for 2013. The list includes the top 23 titles on the social network's platform, and rankings were based on a combination of user ratings, growth, and quality. Games were also separated into three categories: best new games, staff favorites, and hall of fame games, which came out before the start of this year but remain popular.

But the immediate questions that came to mind when this list dropped were, "Did Candy Crush win?" and "Did any Zynga (NASDAQ:ZNGA)titles make the cut?" 

Source: Zynga

Candy Crush didn't win because the game from King -- a company that might soon launch its IPO -- was released before this year. But Candy Crush does make an appearance in the hall of fame. The top best new game instead went to hidden object game Criminal Case from privately owned studio Pretty Simple. 

The top game was surprising, but it would seem wise to assume that Zynga titles made a strong showing. Zynga and Facebook have a well-documented codependent relationship that included Facebook's infamous S-1 admission that Zynga accounted for 12% of the social networking giant's 2011 revenue. But only two Zynga titles made the list.   

Here's a look at the Zynga games that made Facebook's list -- and the expanding competition that poses challenges for the business. 

Zynga's best of the year
Casino game Hit it Rich! Casino Slots was Zynga's sole entry in the best new games list. Here's how Facebook described the title: 

This beautifully designed slots simulation from the FarmVille developer features slot machines based on characters and themes from movies, television, and comic books.

The other Zynga appearance came in the hall of fame title with Farmville 2 -- the sequel to the massively popular farming simulator that made Zynga a household name.

Facebook's list wasn't ranked according to usage metric. But Farmville 2 still performed strongly in that area, with more than 10 million monthly active users, or MAU, according to AppData. And Hit It Rich! Casino Slots had 1 million MAU following its late October launch.

Hit It Rich could become a slow but steady performer for Zynga, which has had good luck with casino titles. Zynga Poker remains the company's second most played game -- and the 15th most popular Facebook game overall -- and the title was first released in 2007.

But Facebook's top-games list shows how much competition Zynga faces from both established and upstart game developers. And a couple of major gambling companies are offering competition for Zynga's tried and true casino titles. 

Crowded field of social gaming
The Facebook list includes eight indie games from companies that most readers wouldn't recognize at a glance. But there's also the bigger players in the mix. King matched Zynga in two appearances on the Facebook list. The company's best new game was Farm Heroes Saga, which continued the "match three" style of Candy Crush Saga.  Farm Heroes currently has 10 million MAU compared to a stratospheric 100 million MAU for Candy Crush, which is the most played game on Facebook.

But Zynga also faces increased competition against its steady casino games. Facebook's hall-of-fame list included Double Down Casino from International Game Technology (NYSE:IGT) and Slotomania from Caesars Entertainment (NASDAQ:CZR).  

Double Down Casino had 1 million MAU and was the driving factor when slot machine maker International Game Technology acquired the original developer for $500 million last year.  And mega casino company Caesars Entertainment didn't want to miss out on the party of real-world gamblers moving into social gaming. Slotomania also had about 1 million monthly MAU.

Zynga had once considered a move into real-money gaming but dropped those plans. So International Game and Caesars both benefit greatly from having larger backing companies built on real-money gambling. But Zynga's casino titles could prove strong enough for the company to hang on until the next charts-busting title emerges. 

Zynga's near future 
Zynga's third-quarter report in late October featured revenue of $203 million, which beat analyst estimates by more than 1%. The company reported a loss per share of $0.02, which was nonetheless 55% higher than the consensus estimate.

But the quarter also marked a turnaround for overall daily active users, or DAU -- a metric that had declined for several quarters. And the average bookings per DAU --or the amount of money spent in game per user -- marked a third quarter of clear improvement.  

Zynga's fourth-quarter guidance includes revenue of between $175 million and $185 million and a net loss per share of between $0.05 and $0.04. Analysts predict revenue of $183 million and a net loss of $0.04.  

Foolish final thoughts
King is Zynga's closest rival in terms of powerhouse titles, but the diversity of Facebook's list shows how it isn't enough to just have one or two popular titles.

Companies need those titles plus slow and steady burners. Zynga has Farmville 2 and the potential of its casino titles. But it will take a few more successes before Zynga can regain its position as the darling of social gaming.