You can spend five dollars on Plants vs. Zombies 2: It's time to venture out of ancient Egypt and into the pirate seas. You can unlock upgrades with cash or use your real money to buy in-game currency, stock up on power-ups and use them to break through each level. Or just keep your money and enjoy an experience that is just as challenging and rewarding as the original.

Fans of the original flower defense game were understandably upset when they discovered that the official follow-up would be released exclusively on iOS, but what really worried people (me included) was the "free-to-play" deal. With so many free mobile phone games failing to achieve a comfortable ratio of playable content to affordable content, it was only natural to think of a game with limited playtime and pay-per-planting.

Plants vs. Zombies 2 is not like that at all.

Instead of alienating fans of the original game by locking content behind profit walls or turning down gameplay for casual gamers, Plants vs. Zombies 2 only looks for players who lack the patience or ability to complete the game on their own.

Take ancient Egypt as an example.

First off, we're here because Crazy Dave, the charming wacky botanist from the original game, wanted to eat a really good taco again and happened to have a hyper-intelligent, time-traveling RV available.

Egypt consists of a main path with 11 levels and several branching paths that are unlocked via keys collected during normal play. As soon as the player has completed the 11th level, a Stargate (no relationship) opens to the next of three epochs available at the start. When you tap the gate, you will see the following screen:

Ah-ha! There is the robbery! But it is not. Not for the committed player Plants vs. Zombies.

Completing this 11th level has another effect. Suddenly, each of these 11 levels is connected with three increasingly difficult challenges – prevent the zombies from passing a certain point on the field, only clear the level with certain plants – something like that. Completing these challenges grants stars, the other key to unlock this Stargate. A real fan of Plants vs. Zombies doesn't need the motivation to unlock the era. You will overcome these challenges because they are there and brilliant.

The basic idea here is the same as in the original. Players harvest sunlight to plant plants and defend themselves against hordes of weird undead creatures. As the game progresses, a new crop of flora will be unlocked (only one plant in the entire game is cash only) and the zombies have evolved accordingly, but the war remains the same.

Mostly. Since plants are unlocked through actions rather than coins (as in the first PVZ), coins are now used to purchase interactive power-ups. You give the players the opportunity to pinch the heads of the zombies immediately. Another allows players to throw zombies in the air and then right off the screen. The third kills her with the swipe of a finger. The interactive nature of powerups is fairly new, but they are expensive to use as well as powerful.

Also new in Plants vs. Zombies 2 is plant food, a special power-up that can be grown on any of your plants to give them a temporary power boost. Peashooters become machine guns and can easily take out a heavily armored enemy. Sunflowers break out with sunlight. Plant food can also be bought with coins, but the green flashing zombies that drop it are frequent enough that it isn't necessary.

Speaking of no need, you can avoid these upgrades as well – they can be found in the normal game as well – remember the branch paths I mentioned? The one behind closed gates? Open the gates and get your upgrades for free. The paths also feature some of the cool new variations on the game, including a fun Memory Match Joint in which players destroy zombies by matching the symbols on the fields they have worn.

I've now made it through ancient Egypt and the pirate seas (with a little help from my wife, I'm just slightly ashamed to say) and am working on challenges to unlock the Wild West. That's about ten hours of gameplay, and I've never felt compelled to pay even when regular ads come up.

It's almost too good to be true. I keep expecting the game to end at medium level and requesting that I hand over some money, but it seems PopCap and EA don't want my money. I can live with it. If they're happy to generate money from players who are too impatient to play Plants vs. To enjoy Zombies 2 to the fullest, I will be able to take full advantage of the splendid game they have sown.