Shares are down nearly 74% since its stock market debut. User engagement has dropped 53% in less than three years according to social game analytics firm dystillr. And its biggest bet — the $183 million acquisition OMGPOP earlier this year — proved a flop. But the company’s biggest problem may simply be the games themselves.

Last year, I wrote about a serious addiction to the city simulation game CityVille, a lost month where I stole moments through the day — even at work — to virtually harvest crops, build businesses, and collect rent. I had become one of those obnoxious Facebook (FB) users who bombarded friends with notifications like “JP needs bird seed to feed pigeons!!”

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The love affair was brief. Four weeks later, I felt like I had done all there was to do. In reality that wasn’t really the case — its team is always developing new missions — but as a player, one who grew up playing traditional videogames, CityVille had become extremely repetitive and well, boring. After all, you can only harvest so many crops before you’ve had enough. And I wasn’t alone in feeling that way. Over the last few months, I began to hear the same thing from people who briefly dug Zynga (ZNGA) properties but grew tired and moved on: The depth just wasn’t there.

As many developers and gamers will tell you, that’s an essential ingredient for a game’s longevity. Some traditional games may offer you as little as 10 hours of gameplay before they’re quickly exhausted; others will offer hundreds. Indeed, there are some games, like 2008’s Grand Theft Auto IV that some will pick up years later. That’s a testament to deep and satisfying gameplay. But with a game like CityVille the fun was fleeting.

Now, it’s no surprise that Zynga is exploring what’s being called “midcore” gaming, a category of gaming that promises more depth than your FarmVilles of the world, and one companies like Kixeye and Kabam have focused on from their outset. Last month, the company announced that it had acquired the midcore gaming startup, A Bit Lucky, all no doubt as part of its effort to seriously boost user engagement. Whether Zynga does that, and does so in time to raise its poorly performing stock, remains to be seen.