Plants vs Zombies is pretty much a sensation. It is out on all platforms I can think of (PC, Mac, iPhone, PSN, xbox360, probably WiiWare) and it's doing very well on all of them. I am not sure why, I mean it's a mediocre tower defense game, although I suppose they are all mediocre.
Definition of Tower Defense via Wikipedia:
Tower defense or TD is a subgenre of real-time strategy computer games. The goal is to try to stop enemies from crossing the map by building towers which shoot at them as they pass. Enemies and towers usually have varied abilities and costs. When an enemy is defeated, the player earns money or points, which are used to buy or upgrade towers.
What makes this game different from other tower defense games? Well it has a somewhat unique resource gathering system. In most TD games you get money from killing enemies, and use that money to build more towers. In PvZ you get "sunshine" by planting sunflowers. They slowly dance, and spit out sunshine balls which you click on to pick up. This is interesting because you are in full control of how many sunflowers to build, and you must build them for "money." Each time you are going to spend sunshine (I will be using sunshine in place of money from now on) you need to decide if you are making defender plants, or sunflowers for more sunshine. I am a fan of making choices and resource tension so I think this is a great system. Also you have limited space and sunflowers take up that space. Other than that it's probably the cute graphics and humorous themes that make this game so popular.
I think the game is great. I had lots of fun playing it. I didn't beat it however. Anytime I don't beat a game, it means that game failed to hold my interest in some way. I know exactly where it went from in this game. The pacing. Each (standard) level starts with you having 0 plants, and 50 sunshine. A sunflowers costs 50 sunshine. So the first flower you plant absolutely MUST BE a sunflower because if you plant anything else you will have 0 sunshine and no income. Okay so I build the sunflower, now I have 0 sunshine and I sit there and watch it dance. I don't know how long it has to dance, I never timed it, it just smiles and wiggles. FINALLY it spits out 1 sunshine, I click on it, +25 sunshine, that isn't enough to buy anything. More waiting. More waiting. More waiting. Flash forward to when I have 5 or 6 sunflowers all giving me 100+ sunshine on a regular basis and finally the game actually begins. This is how every level starts. Maybe 1 or 2 zombies will stumble along before you have your sunshine factory up, and you just plant 1 random defender to kill them.
This is bad design. The first 2 or 3 minutes of every level plays out almost exactly the same! I was on something like level 4-3 when I just couldn't take it anymore. There are so many ways to fix this problem. I can think of three right off the top of my head!
1. Player starts with 250 sunshine, and 4 zombies attack right away.
This would be an improvement because you would be able to make valuable choices right away. You could spend all the sunshine on 5 sunflowers but that would leave you defenseless. You would need to strike a balance of constant income and steady defense right away. It would be tense and exciting. You would have time to plan everything out. It would also give you the option of buying a fancy super plant early.
2. Player starts with 5 sunflowers planted in random spots on the map to kick start the generating.
This is a cool idea because sometimes the sunflowers will be placed in bad spots that are hard to defend, or are to far out in front. They would all work for a short time, but soon the zombies would start eating them unless you put defenses on each one. This would be a fun strategy element because you would need to choose which sunflowers to defend and which to let go.
3. Sunflowers make larger sunshine balls, or generate them more often.
This would simply accelerate the slow pace of the game, although adding little strategy.
I am sure there are more I could come up with if someone wanted to pay me, or seriously ask me to think about it. But this is simple stuff. How did nobody notice that around level 30, planting your first 3 sunflowers is a real drag? This could have been one of my favorite tower defense games. But instead it's just a great example of wasted potential.