In PvZ, you start off on your lawn and you defend your house. As you progress, you earn coins. You use these coins to buy new plants you've unlocked as you make your way through the game. PvZ2 does it slightly differently. You meet up with Dave and he drives you through time to defeat zombies through time. Besides just a change of theme and background, each timezone sport different zombies with different abilities and require different techniques to defeat and different "lawn" layouts.
Ancient Egypt, the level I've played the most, has graves that you have to remove because Peashooters can't shoot past them and zombies can walk unhindered closer to your base. You'll have to use Grave Busters to remove them, while dealing with zombies who steal your sun and zombies protected by sarcophagi. In Pirate Seas, the lawns have planks that stop abruptly and are replaced by sea water. The zombies can't walk on water so they swing across. You'll have to think of how to use the water to your advantage, as well as deal with zombies unaffected by not having land to walk on. The Wild West era has rail track and one cart you can move vertically. It's great, but that means you can only plant 1 thing on the cart that is responsible for the entire length of the track.
Each time zone presents new challenges that keeps everything fresh. Each one also has its own map, with branching pathways that lead to perks and other plants to unlock. Instead of just going through each stage one at a time in a linear fashion like in PvZ, PvZ2 gives you the option to pick which level to do first, as long as you have enough keys.
While we're on the topic of challenges, another new feature of Plants VS Zombies 2: It's About Time is their star reward system. Instead of reaching a particular score per level like in most other games, stars are earned like trophies or achievements. You have to fulfill a set number of requirements per star. That means every single level on each map is a different experience. Challenges range from producing X amount of sun or not planting in certain areas of the map or not spending any sun for a given amount of time or even not losing more than X number of plants - remember, those one-time use plants like cherry bombs count as losing a plant.
Some challenges require plants you can get on different maps and advanced levels so you can't just bullrush your way through. You're gonna have to play through levels you can and come back to previous challenges if you wanna get all the stars. The stars aren't just for show either. You'll need them to move on to the next world.
As for the plants, you'll see some of your favorites return. I'm particularly attached to the Threepeater and the Melon-putt. There are also new additions to the roster, like the Spring Bean and the Snapdragon. As levels and challenges get harder, you're going to have to learn each plant's strengths and weaknesses. The game's built-in encyclopedia should be useful.
The Bonk Choy making quick work of an oncoming zombie mummy thing.
To help out players with the very challenging, but not too frustrating list of requirements for stars, PvZ2 has the Plant Food and the screen manipulation Power Up systems. Plant Food is dropped by defeated enemy zombies and can be used to super charge a plant's abilities. My favorite has to go to the Cabbage-pult especially in the early stages of the game because it hits every hostile force on the screen, even the ones that start past your front line of defense. The Wall Nut gets armor plating and the Peashooter shoots like a Gatling Pea but with a much higher ROF.
Power ups are those three icons you see to the left of the shovel. They cost in-game coins to use and will help you out a lot in a pinch. You can choose to electrocute, or swipe or pinch zombies away from the screen. It's pretty nifty and I'm sure there has come a time in every PvZ gamer's life that they've just wanted to flick those damn dirty zombies off the screen themselves.
To add to the replayability of the Plants VS Zombies 2: It's About Time, PopCap has introduced the Challenge Mode. Every world has it. On your first level, you work with a Peashooter, a Wall Nut and Sunflowers. On the next level, Crazy Dave randomly shows you 3 plants, and you can only pick 1 to use. So, every level you advance, you get to add one plant to your arsenal. Every level sees an increase in zombie variety and difficulty. Lawnmowers and sun money carry over to each level. It's a modified survival mode.
As far as graphics, presentation, and sound design go, you get what you'd expect from a PvZ sequel. If it ain't broke, don't fix it. And thankfully, PopCap did not change too much of the essence of PvZ. The cute 2D sprites are still there but you get upgraded zombie looks. The music is still addictive to listen to and they fit each world nicely. Humor has been a trademark of the Plants VS Zombies franchise and the same pun-loving type of humor is found in PvZ2, for which I am happy.
With Plants VS Zombies 2: It's About Time being a free-to-play game, PopCap has to make some money somehow so they introduced a micro-transaction system. Unfortunately, in a way, this is a pay-to-win system, but it isn't that bad. You can play through the game and get all the stars with what is provided for free. However, if you want to get the full arsenal, you'll have to pay $2.99 per premium plant. I wouldn't be surprised if they add more worlds and challenges through a DLC system.
For the replayability, price (it's FREE!), fun factor and just overall enjoyment, I would give Plants VS Zombies 2: It's About Time a 4.5 out of 5. This is the most fun I've had on a tablet since... well, since Plants Vs Zombies.
Right now, PvZ2 is available on iOS Australia and New Zealand. At least, that's where we got it. You can keep checking if your iOS account has it yet. I highly recommend you pick this one up. It's FREE!
EDIT: Plants VS Zombies 2: It's About Time is now available in multiple regions, including ours. So, ENJOY!