Nate here. over the past several months the most popular games on Facebook nowadays were games like Mafia Wars and Farmville. Apparently they were all made by the same "publisher" called Zynga games. If I recall correctly, their first game was called Yoville, which actually started out with 3D spites, but then changed completely later in a 2D sprite perspective when Zynga made a name for themself later on.
A couple days ago I was a bit bored, so i decided to go all out and try most of their games, Farmville, Petville, Cafe World, FrontierVille, and Mafia Wars (which I was already playing for awhile.) I realized how this was dragging people in after awhile. If you are a Harvest Moon gamer, you'll understand how FarmVille and FrontierVille would be liked by so many people. If you're a Sims gamer, you'll understand how CafeWorld and YoVille would be so popular. It's all about trying to make money and climbing the tree to prosperity. Mafia Wars is a bit different from all of the others, but it has the same focus, only with added PvP elements to it. PetVille, however, is obviously raising a pet and making stuff look nice. I can only imagine how annoying my friends thought it was while I was publishing all of those game feeds from each game. More on that next..
Each game has a system in FB, where if you find an item or something like that, you can publish it to your FB feed, and if other players click on it, they can get the item as well. BUT...if they aren't players, it's just another annoying ad to them, which is the biggest gripe about these kinds of games. Sometimes people just don't like seeing constant feed updates from you..but sadly it can't be helped until they find a way to alternate a way to make it better.
Also Zynga created this toolbar system where it has all/most of its games on it where you can check and see if certain things are about ready to be completed or not, then you can go back and deal with them when the time is correct. Very useful, not to mention the toolbar gives you special bonuses.
Overall I think the Zynga games aren't bad for Facebook games, but I think they can try a little better somehow, like with less feed notifications, but that's just me, they probably can't. They're not bad for playing when you have nothing to do. My recommendations would be playing Mafia Wars , Cafe World, FrontierVille, and FarmVille (in that order of tier.) I give it a 4.4 out of 5.