I played Plants vs. Zombies, and Kingdom Rush, two games in the Tower Defense genre. The core premise of both games is similar: waves of enemies are headed towards your base, and you are tasked with placing towers with different abilities such as dealing damage or slowing enemies down at strategic positions in order to defend your base. But the way both games implement this core mechanic is very different.
Plants vs. Zombies plays out on a board with five or six rows and nine columns, each cell being a spot that we can place defensive plants on (though some maps may have pre-existing obstacles or other cells that cannot be built upon). Waves of zombies attack from the right side of the board. This gives the game a very solid structure with a limited number of possibilities – in most rounds a player places less than twenty plants in the first four to five columns – so much so that the game hardly feels like a strategy game. Plants vs. Zombies seems to emphasize quick in-the-moment decision making to place a new plant or remove a poorly placed one, while waves are already attacking; long-term pre-attack strategies seem to be deemphasized by the randomness in which row the zombies attack from, which means that a symmetric plant base in each row is likely to be an optimal strategy, and so there aren’t certain rows that are clearly better to build in before the attack begins.
Kingdom Rush puts the player in control of a winded path with pre-determined spots where defensive outposts can be built. Paths may have multiple entrances from where attackers appear, but there is typically a single exit that needs to be guarded. Winded paths means that not all placement positions are built equal: for instance, one can create choke points where hordes of attackers are blocked by obstacles and attacked by carefully positioned offensive turrets. Since the entirety of the map is visible, and hordes are typically evenly distributed between multiple entry points, means that pre-game strategy is a lot more important.
Additionally, Plants vs. Zombies has a lot more variety in the types of plants than Kingdom Rush has in defensive units. These plants are unlocked by playing the game further, which means that rounds have a lot more effect on subsequent ones in Plants vs. Zombies, than in Kingdom Rush, where each level seems a lot more standalone.
In terms of the design and graphics, Plants vs. Zombies has more pleasing, cartoon-like visuals, as compared to the bland and somewhat more war-like graphics of Kingdom Rush. This also reflects the distinction between sheer game-playing experience that Plants vs. Zombies prioritizes, versus the strategy game experience that Kingdom Rush tries to create. I think Plants vs. Zombies delivers better on the sensation aesthetic than on challenge, whereas Kingdom Rush is the opposite.