My last app review covered “Plants vs. Zombies,” a fun game made by PopCap, and an easy way to waste time better spent doing homework.

“Plants vs. Zombies 2: It’s About Time” is an evolutionary refinement of the original, not a revolutionary new game. This is good and bad.

The game retains the basic structure and game play of the original game. Players plant plants to defend against the zombie horde.

The game progresses linearly through different levels. Each level brings a new plant or some other element to keep things fresh. The levels are never too hard, so it is easy to feel like you are making progress.

The story takes a twist when the player’s old buddy, Crazy Dave, shows up with a time machine. Crazy Dave just ate the last taco on Earth, and the player is along for the ride as Dave goes back in time to eat it again. It doesn’t really make sense, but it doesn’t have to.

It’s just a thinly veiled excuse to play the game in ancient Egypt, on a pirate ship, or basically anywhere other than the suburban lawn from the first game. Even so, the change in appearance is welcome.

The new gameplay elements also are welcomed. One level resembles the kid’s game “Memory,” but instead of collecting matches to beat other players, the player must make matches to destroy the zombies horde before it overruns the level.

The only bad thing about the new game is the constant distractions. The game has an elaborate system of power-ups, and new levels to unlock that are purchased with coins and gems earned while playing, but players can spend real money to get currency in the game.

I appreciate the game being free to play, and I know the app developers need to earn money, but I prefer the business model of the original game where players could choose from an ad supported version or paid version that was ad free. The constant appeals to spend money for a better game experience in PVZ 2 really feel like the worst combination of these other two options.

Overall, the game is fun though and you will enjoy it if you enjoyed the original.