I don't why people are so focused on the whole free play to thing that they're not noticing that the game is substantially worse than the first one, gameplay wise. Cutting out all the night, water and roof levels that had actually different gameplay and strategies and replacing them with different locations is a terrible idea.
The worlds are pretty much carbon copies of each other, with a few minor differences such as there being a few slivers of water on the pirate stages. You fight the mostly same progression of enemies all over again, as if making the pirate zombie have a wooden bucket on his head is any different than the steel one they have in Eygpt. There are a few world specific zombies which help to make it feel different, but not enough to compensate for the amount of times you'll be playing those levels.
I haven't finished everything yet, but if there's not some sort of mode or option for you to be attacked by a mixture of all the zones zombies, I'll be super bummed out. The end game of PvZ threw literally everything they had at you, wheras the end game of the first two zones is almost identical to the very first stages, except there are one or two different zombie types in there.