The 1.7 update of Plants vs. Zombies 2 is considered the biggest update in the game, since it modified and replaced a large amount of features, as well as adding new content. It occurred before any additional worlds were released, and as a result it only affected Ancient Egypt, Pirate Seas, and Wild West.
Before the 1.7 update, Plants vs. Zombies 2's map worked completely differently.
In each world, there were 10 levels (11 in Ancient Egypt) on the main path, with four or five branching paths along the way. Each branching path contained three Brain Buster levels of one type, and was blocked by a gate that could be unlocked by using keys or by paying real world money. The fifth level of each world (eighth in Ancient Egypt) is the first level of that world's exclusive Brain Buster, with the other three levels behind its Key gate.
After beating the last level on the main path, each regular level on the path had three star outlines added to it. When playing that level, the player could earn each Star by completing goals for success that were added to that level, called Star challenges. Once the player earned the first star by completing the Star challenge that had appeared, the next time they played the level they would play to earn the second star with a different challenge, and the next time the third. If the player failed to complete the challenges in a particular level, they could still continue and finish the level, but they would not earn the star. Stars were also awarded for not losing Lawn Mowers when completing Brain Busters or the final level in each world.
The next world could be accessed by completing the final level in each world (Day 11 in Ancient Egypt, Day 10 in Pirate Seas and Wild West) to unlock the Star Gate, then by collecting a set number of stars, or by spending real money. The worlds had to be traveled to in order.
In the 1.7 update, the levels were all rearranged into a single path with 24 levels per world. One level of each Brain Buster type were removed, and the remaining levels mixed into the path along with the regular levels. Some Star challenges were given their own levels, now requiring the goals to be met in order to complete the level at all. Keys and stars were removed entirely, and coins and costumes respectively were awarded for any the player had collected. The final battle levels in each world were modified and replaced by Gargantuar battles found on the 8th level in each world. Completing them awarded the player with a World Key, which could be used to unlock a world of the player's choice. Every Brain Buster's second and third level dialogue with Dave and Penny were also entirely removed in their present version, however they are still in the Chinese version.
In a later update (the 1.9 update), the 25th level in each world were added, which were the battles with Dr. Zomboss. Only Ancient Egypt - Day 25 was initially available, and the other two became available over the next month and a half.
The 1.7 update also adjusted some features during gameplay.
Sun was worth 25 before the update, like in the original Plants vs. Zombies. Starting with the 1.7 update and up, sun is worth 50. As a result of this, Sunflowers began to produce 50 sun at once instead of 25, and Twin Sunflowers produce 100 instead of 50. However, their Plant Food effects were adjusted so they still produced the same amount, although Twin Sunflowers produced an additional 25 sun with their Plant Food effects. Small suns that were worth 25 were later added into the game and could be produced by Sun-shrooms.
Zombies' spawn rates were adjusted in the 1.7 update, and now spawned faster than they did before. However, recharge times for seed packets were also sped up to counteract this. This was to make levels move along faster as the developers felt levels moved too slowly. In the 1.7 update, zombies waited to spawn right after the "Huge Wave" sign disappears like the original Plants vs. Zombies. Before the update, zombies spawned right when the sign appeared.
The Turbo Button was added, allowing the player to speed up the game even more. It causes everything to speed up when activated, so the player can move faster through more tedious parts of the game, like setting up a sun production at the beginning of a level.
Gargantuars from three different time periods were added, and were encountered in Day 8 of each worlds and in Endless Zones. Imp Mummy was also added as there was no Imp variant in Ancient Egypt for the Mummified Gargantuar to throw.