I've spent some time playing the game over the past couple of days, and my impressions for the game itself and its IAP mechanism is as follows:
Off the bat, I must say this is amongst the most polished games I've seen on Android. Not just the fact it runs smoothly, but that it has got impressive, Pixar quality dare I say, visuals and animations. Loading times are also kept to a minimum.
As for the game itself, it plays in the form of a turn-based strategy title. In your turn, you can pick your own plants and place them on the green. You have a set number of points to spend on each turn, and different plants have different points allocations. So, then the enemy (made up of robots here) advances and your offensive plants will attack them. Your plants cannot move forward...they will always remain stationary.
You start off each game with a small patch of green. So far, I have come across two different game variations (these may be the only two variations, but I can't confirm). One is "kill all robots", which is self-explanatory, and the other is "save the tree", where you have to grow your patch of green using certain plants and let it spread to the parts on the map where the chains bounding the tree are tied up to. Enemies are sometime generated from oil pipes, and to stop them from generating, the same concept of spreading the green applies. Basically, the moment you spread the green to an enemy component, it gets destroyed.
You can purchase plants using gold coins or gems to build your "backyard". Each plant can only be used a set number of times in battle, but this can be increased by "cloning them". You can also evolve the plants to make them stronger.
One major negative is that the game requires Internet connection or it won't even start up! I find this baffling as beyond inviting Facebook friends, there isn't much to do online in the game. Everything is played locally.
IAP mechanism explained:
You can only purchase one of the currencies via IAP, and that is the gems. Gold coins can only be earned by playing the game itself. You do earn some gems by completing the game stages though. Gems cannot be converted into gold coins. Everything in the game is done using gold coins, except buying timer refills, powerups and purchasing Gold or Silver grade plants.
Every game that you play costs 10 timer points. You start off with 30 points. When you level up, this refills fully automatically. Of course though, keep in mind that the further you get in, the less often your will level up. Also, leveling up each time gives you 1 extra timer point. For every 10 minutes waited, you will earn 1 point. So theoretically, if you have only 1 point left, you will need to wait 90 minutes just to play another game. And then wait another 100 to play the next game.
Initially, you level up quickly, so in the first few games, you don't feel the effect of the timers. But by the 3rd mission, if you lose the 3rd game in that mission, you are pretty much screwed (like me). To refill the timer point bar, you need 20 gems. 30 gems can be bought for $2.99 (the cheapest purchase tier). If you forfeit or quit a game, you also lose the 10 timer points.
So there you have it, a stinking implementation of timer-based IAPs from Zynga, runing what otherwise seems like a pretty good game. They really must be having a intra-developer battle with Gameloft and EA to see who can come up with the worst implementation of timers in a game.
PS: This is based on the limited release version of the game. There is a scant chance that Zynga may rework the IAP model here, but generally you get the idea how it will eventually turn out to be.